1/20Th Inch Markings On Ruler

[MTbowels]

I've got an engineer's 12 inch steel rule that has each inch divided up into 1/20th of an inch graduated divisions. Who would need to use such a scale? I do remember using wood rulers at school many years ago that had tenth of an inch divisions marked on it and I never managed to fathom out who would use them either!

Thank you

[Old_Geezer]

People you want to mark out 1/20th of an inch, maybe ? 5% of a whole inch.

[Peter Pedant]

erm people who wished to measure with an accuracy not less than 1/20 "

yeh why have micrometres /um and Angstrom A' when you cant see them ?

[gingejbee]

Just because the divisions are there, it doesn't mean that they need to be used...they are for completeness. Similarly, metric rulers have 1mm.divisions.

[twix123]

Very useful when using scaled down drawings etc.

[Mamyalynne]

I still have a few micrometers we used when we were in the engine reconditioning business - great for a Thou of an Inch etc.

[Obiter]

People in engineering might appreciate this one:

Two guys in the dole queue get chatting. One says, "I lost my job as a fitter and turner because I was six thou out". Second one says, " I lost my job because I was two thou out". First one says,"Only two thou, that's a bit harsh! What was your job?" Second one says, "Club steward".

[alavahalf]

Now we are all metric a 10th on an inch is less likely to be heard of. But before we went metric a 10th was quite normal to use, especially in engineering.
I used to check the bore hole in large pistons .... the tolerance was 2/10 th of a 1000th of an inch.

[MTbowels]

I don't quite understand who and why exactly anyone would want to measure with an accuracy of "not less than 1/20". Gingejbee, what use is "completeness"? Why is it complete with 1/20"? If that were the case, where are the rulers with nineteenths and elevenths of an inch etc ad infinitum?

[stuey]

In the science, if that's the correct term, of measurement there are all kinds of weird and wonderful systems. Take, for example, the sizing of pocket watches: "Watch movements are measured in an arcane English system of measurement called the Lancashire system or Lancashire Gauge**. In this system, 1 5/30th inches is the "base" measurement and is called 0-size. Each 1/30th of an inch adds 1 (or subtracts 1) to this base. A watch is measured through the center of the lower plate of the movement (the dial side). If the movement is asymmetrical, say oval or rectangular, it is measured at its narrowest point. Note that the case is NOT included in this measurement, only the movement. Measuring the dial is usually a fair approximation of the lower plate measurement."

[stuey]

I have a steel rule that my father used to use at work, and one section is divided into 1/100ths of an inch! He's no longer around so I can't ask him if he could see them let alone make use of them.

[Sipowicz]

Stuey, you keep your distance!

[stuey]

That sounds like a familiar refrain, Sipowicz:)

[Obiter]

I'm no engineer but I can remember when I laboured in factories as a student in the hols some people carried a micrometer, which could measure very fine distances.

[stuey]

Here is something else regarding watchmaker's measurements, and also a reference to the OP's question.
"Watchmakers' use
The ligne is still used by French and Swiss watchmakers

There are 12 lignes to one French inch (pouce). The standardized conversion for a ligne is 2.2558291 mm (1 mm = 0.443296 ligne), and it is abbreviated with the letter L or represented by the triple prime, ‴. One ligne is the equivalent 0.0888 inch.

This is comparable in size to the British measurement called "line" (one-twelfth of an English inch), used prior to 1824.[2]"

[stuey]

Sorry, that mentions 1/12 not 1/20 of an inch.

[carrust]

remind me not to get stuck in a lift with stuey:-))))

[tonyav]

I use a micrometer every day, very useful tool indeed ( well it is in engineering ).


Obiter
People in engineering might appreciate this one:

Two guys in the dole queue get chatting. One says, "I lost my job as a fitter and turner because I was six thou out". Second one says, " I lost my job because I was two thou out". First one says,"Only two thou, that's a bit harsh! What was your job?" Second one says, "Club steward".


LOL, like it., Obiter.

[stuey]

Carrust, as a general RULE, I tend not to talk to strangers in an elevator:)

[carrust]

I'll watch out for you then:-)

[stuey]

Talking about measuring, I think that ammunition is measured in 1/100ths of an inch. Any gun type people around here today?