That is a very neat trick... but consider this simple plan:

For the fractional part of the dimension, divide the bottom number into

the top number to get its decimal equivalent.

Example (7/16" = 7 divided by 16 gives you 0.4375 inches)

If there are whole inches involved in the measurement then it becomes

1.4375, 2.4375 etc.

Divide the decimal inch number by .03937 and you have your millimeter

equivalent.

Example ( our 7/16" is 0.4375 decimal inches, we divide it by .03937 and

we have our answer of 11.11125 mm.

Memorizing the number .03937 solves the whole problem going either way,

to or from inches and millimeters.

Let's have an example of going from millimeters to inches:

If you multiply 100mm by .03937 you will get it's equivalent in inches,

100 x .03937 = 3.937 inches.

The number .03937 is simply how many inches are in one millimeter.

This .03937 method was the common way that millimeters and inches were

dealt with in shops I worked at in the US.

tom jobe...

On 12/14/2017 4:02 PM, 'Craig Sawyers' c.sawyers@tech-enterprise.com

[TekScopes] wrote:

On the topic of conversion between Imperial and SI units of length

there is a well known method of

quickly converting aliquot parts of an inch to millimetres using the

approximation 254 = 256

If you have a fractional inch dimension, multiply top and bottom of

the fraction by two repeatedly

until

the denominator equals 256.? Shift the decimal point of top and

bottom one place to the left.? The

numerator now equals the inch dimension times 25.6, which is the

equivalent number of millimetres

(to less than 1% error)

Ian

Darn, that is a neat trick. I really like simple numerical methods

like that.

Craig

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