I've used wFret locally installed on each of my Windows PCs for years to generate both fret placement charts and full size printed layout guides. That program, as well as alternative fret layout procedures and guides are still available on the web archive of my old website
HERE.
Any layout guide that is printed with a home printer needs to be verified for accuracy, but the zero to 12th position is all you need to measure.
I sand off the markings on a 99 cent aluminum yard stick and transfer printed fret layout guides by scribing the lines to the blank aluminum. That way you only need to do it once for any particular scale you might use and you'll have the equivalent of one of those fancy layout sticks that the supply houses tell you that you should buy only from them.
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Sidebar FYI, Skip this unless you need to know or just like to obsess over details.
If you REALLY need accurately printed full size plans, here's the whole story of my adventures that might help if you're going to market your drawings as I did.
I do know a bit about this whole printing issue, as I used to market several different full size plans for several different fretted instruments. It's easy enough to draw them accurately in CAD but more difficult to have them printed. My first attempt having them printed was my local "copy shop", where it turns out that the employees often don't know how to operate their equipment. I gave up on that and went to my local blueprint shop who had really great machines and knew how to run them. The printers at the copy shop were toys by comparison.
Even with a great shop owner and large format industrial printers there were still a few hitches in the process of getting accurate prints. My next step was to download the print drivers from the company that made the printers and save my CAD files in a format using the printer manufacturer's print driver format. That worked reasonably well, but every time I needed another 100 copies of a given print I found that the printer manufacturer's print driver had been updated to a newer version and I had to do through the whole "download, have a print made and verify size" process all over again. This was a bit of a PITA as you might guess.
The shop owner and I found a solution that worked really well for both of us. I simply saved my CAD file (the drawing having an accurate border size dimension) as a PDF and e-mailed the file to the blueprint shop. He then loaded the file, made a test print, and made any small adjustment to the printed drawing's outline box dimension so it matched the size listed on the print's information box.
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Now, for those of you playing along at home, here's a hot tip for printed layouts:
Always verify the measured printout, but if it doesn't match EXACTLY then there are two easy solutions. First, check your printer settings to make sure there is no scaling applied. Many printers have a "No scaling" box to check off in the printing command box. Second, if there's a tiny bit of error, simply calculate how much you need to adjust, set a new "adjusted scale length" in the input box (34.07" as an example...) and re-print. Check the actual print out and re-adjust until your printout is dead nuts on.
(...or simply use the original printout that's 1/16" off at the 20th fret and forget about obsessing over something that just doesn't matter...)
I've been building for close to 50 years and the need for extreme accuracy from any particular measuring device isn't as high as what's being related in this topic. The relative fret distance accuracy is much more important, as the final true vibrating length of the string (which includes compensation) is set by saddle location, normally adjustable. (Ardgedee is spot on in his comment above...)
When building instruments it's important to lay out fret positions
as accurately as you can, all referenced from a single starting point at the hypothetical zero location, and cutting slots
as accurately as you can for each of those positions.
To stress over anything closer than 1/64" just isn't necessary. Most any ruler (or printed layout program) will get you there. There are lots of manufactured rules that will get you that level of accuracy, and I've seen many good examples from some of the eBay sellers, particularly one of the sellers who feature "blemished" rules very economically.
"But don't you want your frets within a few thousandths of an inch?" you might ask. It's hypothetically a great idea, in real life not so much. The whole concept of accurately producing specific frequencies is simply unnecessary when you're working with equal temperament. Any specific note may or may not sound pleasant when combined with other notes and/or other instruments, but that's a whole topic in itself. Scales within equal temperament are by nature unpure, so any misplaced desire to obtain that is well, misplaced. Anyone who works within the field of audio and claims to be able to hear notes that are "off pitch" from a fret that is located a few thousandths from it's "ideal" calculated position isn't "blessed", but "cursed" from that ability. Look at all those examples of "wavy fret" methodology if don't believe that there's not a lot of work going into improving "intonation" of fretted instruments. (There's always someone looking to extract money from an easy mark...)
Again, for all practical purposes, measure, cut, install frets as accurately as you can in your shop and you won't need to feel like you fell short in your work.
Coincidentally, I have a 24" Starrett still in it's original anti-corrosion paper that has been hanging in my tool cabinet for probably 30 years that is on the list of "items that are nice, but I just don't use" to be eBayed.
