The testing should preferably be done in the dial up position to eliminate poise errors as much as possible. The first test is made in heat at 90 Fahr., then in normal temperature of sixty-five or seventy degrees and finally in the lower extreme of 40 Fahr.
When the watch is removed from the cold box it will be covered with moisture which will immediately begin to condense. The time should therefore be quickly noted and the watch replaced in the higher temperature box for four or five hours to become thoroughly dry and prevent against rusting of the steel parts.
12. _Rating Card and Method of Calculating Variation._
A card ruled similar to the cut shown in Fig. 3, may be used for entering the rates and the watch need only be set at the beginning of each test, as deductions can be made from the entries on the card and the variation accurately ascertained without resetting or disturbing the time.
Details as to the methods to be followed would be about as follows: Wind and set the watch to correct time, place it in the heat box and at the end of twenty-four hours enter the variation from correct time in the upper left hand square of the card.
a.s.suming that the time is four seconds fast, enter this as shown in the first column Fig. 3, then wind but do not set the watch and place it in normal temperature and at the end of twenty-four hours enter the total variation noted in the second square of first column. a.s.suming the time to be just correct, place a zero as shown. Next wind the watch and place it in the cold box, and a.s.suming that the variation is sixteen seconds fast at the end of twenty-four hours, enter this in the lower square of the first column as shown in Fig. 3. The watch is next placed in the heat box to dry and the variation shown in the three sets of figures in first column are carried out as follows.
Fig. 3
+--------------------------------------------------+No. .................... Make...................+--------+-----+-----+-----+-----+-----+-----+-----+HEAT+ 4+ 4+ 2+ 2+--------+-----+-----+-----+-----+-----+-----+-----+NORMAL0- 4+ 6+ 4+--------+-----+-----+-----+-----+-----+-----+-----+COLD+16+16+ 8+ 2+--------+-----+-----+-----+-----+-----+-----+-----+ 12 0
In the upper square we find +4, enter this in upper square of second column at its full value as shown.
Next we find a "0" in the second square of first column, and as this is a loss of four seconds from the entry shown in the square above we carry it out in second column as -4. In the lower square of first column we find +16 and as this is a gain of sixteen seconds over the square above, it is necessary to carry this to second column at its full value as per ill.u.s.tration.
To determine the extent of variation between heat and cold, simply ignore the normal rate of -4 in the second column and subtract +4, from +16, which indicates an error of twelve seconds slow in heat compared to cold.
Or it may be determined as twelve seconds fast in cold compared to heat. For convenience sake it is advisable to form the habit of using one of the temperatures as a unit for comparison and wherever large quant.i.ties of watches are adjusted, it is generally the custom to use the higher temperature for this purpose and the rate is stated as either slow or fast in heat. In this instance the rate is slow in heat and it will be necessary to shift one or more pairs of screws toward the cut as explained in Chapter 1, No. 2.
13. _Value of the Normal Period Rate._
The rate in the normal period cannot be considered as of any value, its importance consisting only of allowing the metals to return to the natural form and tension before being placed in the cold box.
This is quite important in obtaining a true estimate of the error, because of the fact that in transferring the watch immediately from the extreme of heat to the extreme of cold, there will be a period of time during which the metals are readjusting themselves to the natural form, and the variation in time during this period will not be accounted for, as the real comparative rate will not begin to develop until after the natural form and tension is reached.
If the limit of time devoted to testing is no object and if a very fine rate is desired the observatory method is of course to be preferred. However, by allowing an intermediate day at normal temperature we have the a.s.surance that the hairspring is at the same tension and that the balance has the same form concentrically when the test begins in cold that it had when the test began in heat.
As the object is to find the variation between the two temperature extremes the estimate will be quite close enough and allows the saving of many days" time. Some authorities advocate in addition to the five days required for observatory testing in each temperature that the watch be subjected to an intermediate day in each, instead of in normal, before considering the daily rate. This seems very logical, as the time noted each day would be taken at the actual extremes in both instances and any outside factor in the timing would be eliminated.
14. _Definition of the Characters Used on Rate Cards for Gain or Loss in Time._
In making entries on the rate cards and in figuring the variations the sign + is used as denoting that the watch is running faster than the standard time and the sign - is used as denoting that it is running slower than standard time.
This is stated for the reason that in some instances, generally foreign, the signs are used in reverse, or as indicating that the watch requires a correction of + or - the number of seconds indicated, to attain the correct standard of time. When the signs are identical in a column it is necessary to subtract the lesser from the greater and the result is the variation. There are often instances however, when one rate will be + and the other - as shown in second column of Fig. 4, and in these instances it is necessary to add the figures to obtain the variation.
The first column is always the progressive rate and the second column shows the variation carried out. This example shows +8 in heat, the normal rate in the second square is not considered, for the reason previously explained and the rate in cold is shown as -1. The total variation between the extremes is therefore arrived at by adding +8 and -1, which in this instance gives us a total of nine seconds fast in heat.
Fig. 4
+--------------------------------------------------+No. .................... Make...................+--------+-----+-----+-----+-----+-----+-----+-----+HEAT+ 8+ 8+--------+-----+-----+-----+-----+-----+-----+-----+NORMAL+20+12+--------+-----+-----+-----+-----+-----+-----+-----+COLD+19- 1+--------+-----+-----+-----+-----+-----+-----+-----+ 9
15. _Increasing or Decreasing the Extremes of Temperature._
The extremes of 40 and 90 Fahr. have been used for the reason that they are best suited for general purposes. When it is known, however, that a watch is to be used in a warm climate the extremes may be raised five or ten degrees to advantage. If the watch is to be used in a cold climate, the extremes may be lowered this amount. The metals, however, can only stand the strain of expansion and contraction to a certain degree, and still maintain the positive qualities. Therefore it is quite important that the extremes be not raised or lowered very much beyond these figures.
CHAPTER IV
SOME PRACTICAL METHODS OF CORRECTION
16. _Example of Maintaining a Pleasing Appearance of the Balance._
In altering the location of screws during the temperature adjustment it is often possible to either mar or improve the appearance of the balance. As a demonstration of this point the correction made in regard to Fig. 3 is a.n.a.lyzed. The balance had twelve screw holes in each rim, with the s.p.a.ce between the first and second holes from the arms equal to double the s.p.a.ce between any other two holes. There were seven screws in each rim, equally divided as per cut Fig. 5, which indicates screws in the first, second, fourth, sixth, eighth, tenth and twelfth holes.
[Ill.u.s.tration: Fig. 5]
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 circ.u.mstances however would have caused a ma.s.sing of three pairs of screws at some point and a vacant s.p.a.ce 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.
[Ill.u.s.tration: 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.
18. _Over or Under Compensation._
On some occasions it will be found impossible to maintain a pleasing arrangement of the screws because the temperature variation will make it necessary to ma.s.s all of the screws either in the holes nearest the cuts or in those nearest the arms.
This is due to either over or under compensation of the balance. Over compensation is caused by too large a proportion of bra.s.s in the rims, which causes them to curve inward too far at the free ends in heat and outward too far in cold. When the extent of this error is so great that the rate is still fast in heat, with the screws ma.s.sed in the holes nearest the arm, a correction can be obtained by fitting heavier screws in the holes adjacent to the arms and lighter screws in the holes nearer the free ends.
When the rate in heat is slow with the screws ma.s.sed at the free ends of rims the balance is under compensated, which is caused by too large a proportion of steel compared to the proportion of bra.s.s in the rims. This prevents the free ends of rims from curving inward far enough to carry the weight the proper distance toward the center of balance. A correction for this can be obtained by fitting heavier screws in the holes adjacent to the cuts and lighter screws in the holes toward the center of rims.
In changing the weight of screws as stated above it should be remembered that the gross weight of all screws must remain the same or the timing will be seriously affected. It is also important that the poise be tested whenever a considerable degree of alteration is made, as this will a.s.sist in obtaining an accurate rate.
19. _Special Corrections for Over or Under Compensation._
Balances having the extreme degree of over or under compensation will seldom be found in high grade watches. In any instance, however, it is possible to obtain a better distribution of the screws by fitting either a larger or a smaller hairspring. For instance, we will a.s.sume a case of under compensation in which the screws have all been ma.s.sed at the holes nearest the cuts. If the spring has seventeen coils, a correction of from five to ten seconds can be obtained by selecting and fitting a spring of the same make that will have eighteen coils, and the correction obtained will permit of shifting one or two pairs of screws back toward the arms.