Lou---You are correct, but the number 40 although it has a steel top plate does not match in design, nor does it have a pat. date. No. 401/2 has a nickel finish, 41 has sheet brass top plate, 41 1/2 has a thick cast brass top plate and 42 is all brass. This level does not match any of them??? The June 23, 1896 date appears correct and it is by traut relating to a method of marking the tubes.