This is an oblique response to the question on the accuracy of
Starrett Combo Squares v. other manufacturers.
Although the Starrett is a first rate combo square, it still cannot
compete with a good quality try square in terms of repeatable accuracy
over the life of the tool, due to that fact that it has moving parts
that are subject to wear.
The Marples 9" "Shockproof" (no longer manufactured - r.i.p.) was
manufactured to conform to the British Standard 3322 of +- 0.01mm per
cm of blade length. (El Sauro has its mate and can check it against
his Athol Collection).
The Ulmia has a stated tolerance of +- 0.10mm over the length of the
I've used both of these try squares for a number of years and reach
for one of them to check squareness of cut rather than for the
Starrett Combo Square.
For machinery setup I use a Starrett No.20 Engineers Square.
I periodically check these squares, using a Starrett No.380
Machinist's Straightedge as a reference and have never had a need to
The point, as it relates to the question of the OP, is that it is
cheaper to manufacture a dead on try square than a dead on combo
square and the try square provides a third, economical option to the
Starrett v. Other Manufacturers dilemma. (remember, even god never
made a square johnson)
I fear that the preferential usage of the combo square over the try
square is a direct result of the influence of Brother Norm and his
We should seek to overcome this influence, insofar as we aspire to the
heights of craftsmanship implied by the search for accuracy that must
be measured in angstrom units and its application to a material whose
deformities are measured in fractional inches.
I remain, tongue very much in cheek,
Y.O.B. (yer obstinate bastige)
Thomas J. Watson-Cabinetmaker
Gulph Mills, Pennsylvania