122-inch caliper - photos

[mklotz]

If the work piece and measuring tool have the same or similar coefficient of expansion, would the measurement be off by that much? Assuming both were given time to adjust to the temperature and the designer was competent enough to take it into consideration. That's a lot to assume, of course. Not questioning your math at all. Just genuinely curious about your thoughts on the subject.

Unless you can get everything - room, tool, object - to the same temperature as existed when the calibrations were applied to the tool, your measurement could be off by as much as thousandths of an inch. That might be problematic. If you're trying to hold a succession of parts to the same size (and absolute size is not so important) than, assuming isothermal conditions are maintained, the calipers are useful. For absolute measurements, you can never be sure of your measurement accuracy.

My point was that you never really know the length of your yardstick. That fact has to be taken into account in your use of the tool.

Given that we now have high accuracy laser interferometer tools, I doubt that this tool has much of a market.