Guest gangte -

It shouldn't make a lot of difference whether your instructions are in "English" units or SI, since much of the basic stuff in making an instrument from someone else's plans is a matter of tracing patterns that have no dimensions. If you have an instrument similar to what you want to build, you make the measurements using whatever "units" you want, and make your new one to the same, or similar dimensions.

For most of the things that are "critical," and actually require something to be to specific dimensions, you seldom "measure" the dimensions, you use the part it has to fit, and "match" the mating part(s) to it.

I have a little difficulty visualising how one would follow a video to make something as complex as a guitar, although with a few printed patterns for the big parts I suppose it could be done. If you really want to "study up" and have instructions you can lay out to follow in more or less step-by-step manner, there are several fairly good "textbooks" on guitar making.

Guitarmaking: Tradition and Technology, by Cumpiano and Natelson, Chronicle Books, © 1993, ISBN 0-8118-0640-5, is a paperback that's fairly common in book stores for about the last 10 years that gives pretty complete instructions for Steel-String Folk Guitar and Classical Guitar construction. The $30 (US) I paid for it a few years back makes it a fairly "pricey" book, but you'll likely break enough $50 pieces of fine wood if you don't have good instructions to make it worthwhile having it, or something like it.

For the more ambitious, Making an Archtop Guitar by Robert Benedetto © 1994, Centerstream Publishing, ISBN 1-57424-000-5, has pretty good instructions. It was about $40 (US) a few years back, but probably worth it if it saves even a few mistakes with that first set of materials.

If you're serious about building something that looks and sounds like a convential good quality instrument, it's critically important that you locate a supplier you can deal with for all the bits and pieces of luthiery materials and tools you're going to need. If you find one that's more or less local, they'll probably speak "your kind of units" for everything you need. The instructions are more for the pictures, so that you understand the principles than for getting specific dimensions of stuff. You build to fit the materials at hand, and/or "trace a pattern," at least for a beginning effort.

If you're going to build an "unconventional" instrument, it's your plan - and you supply the units. You may still want a book for the examples of tools you need (and may have to build), how to make a glue-jig, how to set purfling, how to bend sides, etc, that you can get from the instructions.

John