A correction of the rate could have been obtained by shifting the screws in either the sixth or eighth holes forward three holes. Or those in either the first or second holes could have been shifted to the ninth holes and those in the fourth holes might have been shifted to the ninth holes with good results possible in either instance.
Moving one pair of screws under any circumstances however would have caused a massing of three pairs of screws at some point and a vacant space of three holes at another point which would not present a very good appearance for high grade work. Therefore the alteration made was to move the screws from the second to the third holes, fourth to seventh, and from the eighth to the ninth holes as indicated by the positions shown in Fig. 6.
Fig. 6
Examination of the fourth column Fig. 3, which gives the result of the second test will show that the desired correction was obtained with a better appearance of the balance than would have been possible if only one pair of screws had been shifted.
In following the logic of the alterations made we must consider that the screws moved from the second to third holes made no correction, due to the fact that the balance rims remain almost stationary at this point, the alteration being for appearance only, those moved from the fourth to the seventh holes were estimated for a correction of seven or eight seconds only, for the reason that the alteration did not carry them beyond the center of the rims where the greatest curvature takes place. The screws moved from the eighth to the ninth holes however were estimated for the full correction of four or five seconds which is to be expected through shifting a normal pair of screws from one hole to another beyond the center of the rim on sixteen or eighteen size balances. In moving a pair of screws one hole between the first quarter and the center of the rims, a correction of from two to three seconds can be expected and from the center to the cut the difference for one hole is generally four or five seconds, while an alteration between the arm and the first quarter seldom yields any correction.
The matter of appearance should at all times be respected, for it is just as easy to obtain results in most instances and also have a well-appearing balance. There is also less disturbance of the poise usually in moving several pairs of screws a short distance than there is in moving one pair a longer distance.
[17.]Correction Varies When Screws are Above or Below Normal Size and Weight.
Normal corrections can only be realized when normal screws are shifted. Some balances have one half, or quarter head screws which of course will not produce a correction as great as will be obtained by shifting regular screws. Sometimes platinum, or other extra heavy screws will be found in balances and these will produce a correction almost double that of ordinary screws of the same size.