I just use my hand - full span is approximately 9" and I interpolate/estimate smaller distances. It's close enough for large-format black-and-white bellows compensation, probably not for chromes.
Back in the day my Father did excellent close-up and macro work with an AsahiFlex IIa with tubes and bellows. Since the 'Flex had no TTL metering he calculated the exposure factor based on the distance of the extension, measured usually with the sum of the markings on the tubes or bellows, then used a pocket slide rule for the computation. IIRC he sometimes found a tape measure quicker, expecially with the bellows.
Never for MF, but there is always a tape measure in my LF kit for calculting bellows factor. The larger the format, the sooner you need to use it, even if you're not doing macro shooting. (i.e 1:1 on 35 is just someone's eye filling the whole frame, whereas 1:1 on 8x10 is a close headshot.)
In practice I use tubes / bellows (in combination with a right-angle finder) on ILC SLR systems. Close-up filters for fixed-focus / viewfinder / non-ILC cameras are pretty much the only option and I typically use them with a dedicated measuring chain (e.g. Minolta 16) or guesstimates based on finger span, reach, etc based upon the correction factor of the filter in use.
I picked up a set of Polaroid-branded close-up filters some months back at the local antique mall whose case contains a built-in tape measure demarcated with field size, camera focus, and and close-up filter settings. While not particularly useful for how I use the filters, its still a very useful piece of kit that adds versatility to an otherwise crippled camera.
I just use my hand - full span is approximately 9" and I interpolate/estimate smaller distances. It's close enough for large-format black-and-white bellows compensation, probably not for chromes.
I did it with a very narrow metric tape rule at one time, with my own supplemental marking on it. Strictly view camera bellows applications for close-ups. Then I switched over to the Calumet magnification target, which made life a lot easier. With MF or Nikon close up ext ring copy stand applications, I use TTL metering and a gray card.