Why not just buy a metric tape measure and work in metric?

It's only difficult if you do conversions. Why fight it? I did for a long time, but eventually I just bought a metric tape and actually found it easier.

Think about this: Take half of oh, say, 210 mm. OK, 105. Now, add 22 mm thick plywood to that measurement. OK, now it's 127, right? Easy.

Now think about this: Take half of 8 17/64" (EQUIVALENT TO 210mm) and get ______? Now, add 3/4" to that and get _____? Quick now...what are the answers?

Yeah, see my point? Be more Zen like. Don't fight it.

Starret makes a 4 meter/12 foot metric tape measure and I'm sure other companies do also.

22 mm. plywood would be about 7/8th" plywood. 25mm would be very close to 1" plywood. Apparently, Lowther does not want you to used 18 mm (or 3/4" plywood) for these designs.

In metric, it would be easy to ajust for the differences in dimensions betwen the 22mm and the 25 mm. But, not so easy when using English standard measurements.

I'd love to know how these turn out for you because I've been interested in the DX-3 myself for quite some time now.

Should you need any help with the woodworking details I'd be happy to give you my phone number and we could discuss. I've been a cabinetmaker all my life.

Regards,
Mark