In article ,
says...
There's a considerable difference between .0079 and .0157 :-).
In fact, it is different by a factor of 2. (That was a hint!)

The approach being discussed was to make one half-way between, and
sell it as a .0079" oversized 25mm chisel or a .0079" undersized 1"
chisel.

Ah, so. I guess I looked at the table headings and the halfway wasn't
apparent from that. I guess it's me that needs remedial reading :-).

But IIRC, my Sorby chisels are right on for one measurement - inches I
think, but it's been several years since I bought them and checked.

--
Homo sapiens is a goal, not a description