  At the Tevatron the transverse mass is used to separate on mass shell from
off mass shell W production; and the rate of off mass shell W production gives
a measure of the W width. We look at alternative variables to see if the
separation of on and off mass shell W's can be improved, and hence give a
better measure of the W width. We find that the transverse mass is very close
to the optimal variable for separating on from off mass shell W decay, and
hence there is little to be gained by using other, more complicated, variables.
This happens because if the transverse mass is above the W mass, the W is
guaranteed to be produced off mass shell.
