What does the mysterious constant marked by C on a slide rule indicate?
up vote
68
down vote
favorite
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
659214
|
show 7 more comments
up vote
68
down vote
favorite
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
659214
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 7 more comments
up vote
68
down vote
favorite
up vote
68
down vote
favorite
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
659214
Years ago, before everyone (or anyone) had electronic calculators, I had a pocket slide rule which I used in secondary school until the first TI-30 cane out.
Recently I dug it out. Here's a photo of one end of it.
As you can see, there's a number $C$ marked at about $1.128$ (times some power of $10$; with a slide rule you supply that yourself) on the C and D scales. Reading across to the A scale, its square is about $1.27$. By the C1 scale (which reads reciprocals of the C scale) its reciprocal is about $0.886$ (times some power of $10$).
The only two special numbers marked are $C$ and $pi$.
I'm not sure whether it's some frequently used constant that's used (eg) in some branch of engineering, or a number which is useful for some trick for using the slide rule.
Unlike $pi$, which is marked on most of the scales, this mysterious $C$ only appears on the C and D scales, which are the main ones used for multiplication and division.
If you need me to, I can give more explanation of the various scales on the rule and how calculations are done. That might give some clues as to what $C$ is for.
I'm sure the instructions explained what $C$ was, but I last saw those in the 1970s.
Has anyone any idea what $C$ is and why it would be useful on a slide rule?
notation math-history constants
notation math-history constants
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
659214
edited Nov 30 at 14:22
muru
1337
asked Nov 30 at 2:56
timtfj
659214
edited Nov 30 at 14:22
muru
1337
edited Nov 30 at 14:22
muru
1337
edited Nov 30 at 14:22
muru
1337
1337
asked Nov 30 at 2:56
timtfj
659214
asked Nov 30 at 2:56
timtfj
659214
asked Nov 30 at 2:56
timtfj
659214
659214
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 7 more comments
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29
@shoover - good one!
– davidbak
Nov 30 at 19:29
|
show 7 more comments
1 Answer
1
active
oldest
votes
up vote
75
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.7k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
add a comment |
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
75
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.7k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
add a comment |
up vote
75
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.7k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
add a comment |
up vote
75
down vote
accepted
up vote
75
down vote
accepted
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.7k352130
I found the answer by googling "slide rule markings"! It took me straight to the Glossary of the International Slide Rule Museum, which gives C its own entry:
C - Gauge mark found on the C and D scales denoting $sqrt{4/pi} = 1.128$ for calculating the area of a circle and the volume of a cylinder. Place the C mark on the C scale over the diameter of a circle on the D scale. The area of the circle is found above the index on the A scale. If this is the base of a cylinder, without moving the slide, move the cursor to the height of the cylinder on the B scale. The volume is read on the A scale. This gauge mark was rendered obsolete with the advent of multi-lined cursors.
And there is, of course, so much more at that site.
answered Nov 30 at 3:10
TonyK
40.7k352130
answered Nov 30 at 3:10
TonyK
40.7k352130
answered Nov 30 at 3:10
TonyK
40.7k352130
answered Nov 30 at 3:10
TonyK
40.7k352130
40.7k352130
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
add a comment |
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
Amazing. Like a moron I googled 1.128 and didn't get anywhere.
– Randall
Nov 30 at 3:11
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
I've just tried calculating $sqrt{4/pi}$ on the slide rule and the result does line up nicely with the $C$ mark, so this is definitely it!. Thanks!
– timtfj
Nov 30 at 3:23
8
8
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
The museum is amazing! I feel much younger now (maybe that such a musem can make me feel younger should make me feel old...)
– Francesco
Nov 30 at 5:32
1
1
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
@Francesco "It makes me feel like a kid again, and that just reminds me how long it's been."
– Nic Hartley
Nov 30 at 22:01
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
I wish I had that mark on my slide rule. I am always calculating the volume of a cylinder at the beer joint. But calculation of the volume of a Starbucks cup is best done with Simpson's rule.
– richard1941
Dec 5 at 4:10
add a comment |
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Please tag as appropriate—I'm not sure if the right tags and can't yet create a new "slide-rules" tag.
– timtfj
Nov 30 at 2:59
1
Funnest question in forever.
– Randall
Nov 30 at 3:03
Did anyone else here buy their kid a slide rule when he/she went off to engineering school. My daughter ended up with two (we are a family with many engineers). She dutifully sat through my instructions on slide rule use (twice), but I don't think she paid any attention.
– Flydog57
Nov 30 at 17:34
3
Shouldn't this go in retrocomputing.SE? ;-)
– shoover
Nov 30 at 18:34
@shoover - good one!
– davidbak
Nov 30 at 19:29