This yellow plastic caliper is lightweight, reasonably durable (I lose it before it wears out) and pocket-friendly (only 4 inches long). I use it frequently during house or auto repairs to ensure the right size replacement part (such as nuts and bolts, or o-rings and sealing washers) comes home with me from the store or junkyard. I find this easier, quicker, and more accurate in many cases than using a small rule. It is not a precision machinist’s instrument. However, in most of the work I need to get done, measurement to the closest 1/32 of an inch or 1 mm will get the right part or a fit which is good enough to work.
A cool tool is anything useful that is superior to comparable items. If you think this tool is inferior suggest a better one. You are welcome to insult a tool, but comments containing insults to individual people will be deleted. Corrections of fact are always welcomed, if stated politely. Recommendations of better tools are dearly wanted and may be elevated to the front page.