All photos courtesy of Unsplash
In the process of sorting through some items last week I came across some unusual rulers. At a cursory glance, nothing appears to be out of the ordinary, but a closer look reveals two lines of 12 inches on the top face. Both begin at the same mark, but finish in different positions.
Someone I know tried making a box with the help of one of these rulers. He took a tape measure and carefully marked the cutting position of one side then used the ruler to mark out another. When all was done, the box was screwed together, but the lid didn’t fit — the box was out of square. Taking the tape measure to each of the sides, the discrepancy was soon discovered but it took a little longer to realise it was because he had used a ruler with a different inch.
My rulers were from grandpa. He was the sort of person who shined his shoes every day before going to work and oiled and polished his tools once a week. He was able to craft things out of wood near perfect because he was a ‘patternmaker’. Whilst much of this is done today with the help of computers, years ago, when a manufacturer needed a metal object to be reproduced a large number of times, a mould would be used and this was made from a ‘pattern’. One complication with this task is that molten metal shrinks on cooling, so the pattern had to be slightly larger than the finished object. To save the patternmaker from performing these calculations whilst working, a patternmaker's ruler would be used with the shrinkage rate already accounted for, hence the larger inch.
