—— 202 — 
to examine work that lias been previously examined. 
XIII. Make as few variations as possible. 
In repetition there is economy. If two castings can be made from one new 
pattern they will cost less than if they require a new pattern made for each of them. 
Again, if the two castings are slightly different from one another, the pattern can 
probably be made to suit both with a slight alteration, in which case the two castings 
will cost less than if they are designed so that they will require two whole new 
patterns» A* saving is effected if tlie two castings can bo designed alike witliout 
inconvenience, instead of opposite hand to each other, as, even if each does not 
require a separate pattern, the time taken by tlio moulder in taking the pattern for 
alteration to the pattern maker, and the time taken by the pattern maker in altering 
the pattern is entirely lost. Very often castings can bo designed by the careful 
draughtsman to be cast from one pattern slightly modified to suit each case, and by 
this means unnecessary expense saved. . 
Rivets of equal pitch cost less to mark off on template than if of unequal pitch ， 
since the layer-off lias to set bis dividers once in the former case, and a number of 
times in tlie latter. Adopting tlie same sized rivet or bolt throughout a structure is 
often elieapor than varying tLe size to suit theoretical requirements, as tlie additional 
labor in changing punches, drills, cores, etc., tlie additional handling and liability to 
err, in the latter case are more costly than tlie waste of material in the former. This 
principle of tlie economy in repetition is of tlie greatest importance and cannot be too 
widely studied.’’ 
