METHODS OF DETERMINING TOLERANCE. 39 
made at a time. The photometer is made of aluminum; it weighs 
but a few ounces and may be conveniently carried in the pocket. 
The sensitive paper is a commercial printing paper sold on the 
market as “solio.” The photographic paper, the most convenient 
size of which to use in the photometer is the 8 by 10 inch sheet, 1s 
cut into strips one-quarter of an inch wide. The strip is placed in 
position on the shoulder of the photometer so that the two ends meet 
Fic. 7.—Clements’ photometer. a, Perspective view of the photometer in use; b, rear 
view of the inner case; c, perspective view, showing the inside construction. 
at H’, care heing exercised that the strip fits into the groove all around. 
The strip is then drawn tight and the ends are wedged into the slit 
with a piece of cork. 
In this way Clements dispensed with the “normal paper” of 
Wiesner. He has also done away with the “normal shade,” substi- 
tuting for it what he calls a “ multiple standard.” This “multiple 
standard ” consists of a strip of paper exposed for 1, 2, 3, 4, and 5 
seconds successively, thus producing a series of shades. For the unit 
