Fortunately I have the plans for the Steltman Chair. These come from the how to build Rietveld book (see below post).
Here's the first page:
It took me a few minutes to look at the dimensions and understand what was going on. I've never heard the term "to the gain" before. A short translation: "a.(1x) 44 x 100 x 635 (back post, 600 to gain)" means A is the name of the piece, (1X) means you'll need one of these, 44 x 100 x 635 is the size in MM of the piece that you start with. The "gain" size is shorter, meaning the size (in this case 600) is the FINISHED length. The The extra 35mm is the size of the tenon that inserts into the matching piece of wood.
Here's the second page, and I have added dimension conversions from MM to inches: (if you notice a mistake in my calculations please let me know!)
Here is an exploded view of the chair, with each piece labeled:
My wood supplier wont have my wood until next Sat, so in the meantime I will get some other items together...