1/40th rule

[rhohf@idcnet.com]

I asked this question a couple of years ago and got no response.  With the
"old timers" in the expanded membership, maybe someone can shed some light on
this:  apparently the "1/40 rule" refers to the predominant practice in
factories of setting the downbearing at 1/40th of the string tension.  This is
accomplished by setting the string-bridge deflection angle at 1.5 deg.  Does
anyone know the origin or anything else about this?
Any references?

Bob Hohf
Wisconsin