The bottom of the tank should be slightly higher on one side than on the other, with a one-half inch drain pipe fitted to the low side. The inlet end of the pipe should be covered with a fine screen to prevent dirt from accumulating in the pipe and the outlet may be either at the extreme bottom or on one of the sides as shown in the cut. The upper part or cover of box should be made so that it can be easily removed for filling and cleaning the tank.
CHAPTER III
DIFFERENCE IN OBSERVATORY AND COMMERCIAL SYSTEMS
[10.]Observatory System.
In the foreign observatories where watches are generally tested for competition prize, or certificate purposes, they are subjected to either three or five day tests in each temperature, preceded by one intermediate day at normal temperature which is not considered in making the deductions. The purpose of this is to allow the metals to assume the natural condition before being placed in, or changed from, one degree of temperature to another. After the three or five day test, according to the grade of the watch, the average of the daily rates in each temperature is considered in making the comparison and arriving at the total variation. The total error is then considered in the summary, as a fraction of a second variation per each degree of temperature. As an example we will consider that the total error between the two averages is five seconds and that the difference in the two extremes of temperature was fifty degrees F. The variation would be given as one-tenth of a second per each degree of temperature.
[11.]Commercial System.
In manufacturing watches for commercial purposes, both foreign and domestic, the tests are generally made for twenty-four hours in each temperature and the difference in the rates is considered as the total error.
Sometimes preliminary tests of four or six hours in each temperature are made to obtain an estimate as to the extent of error, then alterations are made, after which the watch is subjected to the regular twenty-four hour test. There is nothing to be gained by this in regular work, although for a special rush job a day's time may be saved. Watches are always expected to be in first-class condition and such features as close fitting pivots or dirty oil will prevent any dependable timing. It is also advisable to time them closely before the test is made, as too great mean time variation may confuse in estimating the error, especially if the time is not taken in each temperature exactly at the end of twenty-four hours.
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.