Part 2 (1/2)
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
+--------+-----+-----+-----+-----+-----+-----+-----+
NORMAL
0
- 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 s.h.i.+ft 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.