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Scary ruler discovery

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I was cleaning my work table and placing items in their proper areas.

I have four metallic rulers, both showing the metric and imperial units.

By pure curiosity I placed the shortest one,  15.24cm  - 6" next to my 30.48cm  - 12" and my two 45.72cm  -18" and found differences.

None measured as the other.

The difference is so slight, but could probably cause error when mixed.

Now I marked the 15.24cm and 45.72cm that are almost identical.

The other two to be donated to friends 3rd grader school kids.


A high quality digital caliper needs to be purchased. 

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Sinan, but first check the caliper is accurate first ;)  Mine were out and I have just invested in a "Certifed" digital readout Caliper.


Per, the other trick is to check them for straightness.  I believe the check is done by using one edge to draw a line then flip the ule vertically (same edge but running the other way) and draw another line over that and see if they are coincident - repeat for the other edge.  I use a square or solid base to rest the ruler on but you need to be sure the bases (short edges) of the ruler are square also.  There used to be a good write-up on MSW 1 ... another lost  .... :)





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