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.
Assuming 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. Assuming the time to be just correct, place a zero as shown. Next wind the watch and place it in the cold box, and assuming 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.
| 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 illustration.
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 quantities 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.