Highland Pairos (in F03rf.251$ firstname.lastname@example.org) said:
| I assumed that it was necessary for setting a triangle 90 deg to a
| t-square that is set along the edge.
In the time before CAD, drafting machines, and sliding parallel rule,
the sides were the reference edges for T-square use. The T-square
registered against the side of the table and triangles then rested
against the T-square. The better tables were fitted with inlet steel
channels for the head of the T-square to bear against.
As Leon points out, a pencil ledge at the bottom of the table is
really uncomfortable; and after breaking enough pencil leads, one
learns to put things down so they don't roll. For those who had
learning disabilities, there were all kinds of anti-roll/anti-skid
accessories that could be bought.
For the kind of work that might still be done manually, it might be
worth DAGS for "taboretr" (I found
d_taborets.htm>). These are small rolling carts that hold and store
art paraphernalia. Building one of these little critters has been on
my want-to-do list for a long time.
DeSoto, Iowa USA