THE MIDDLE TEMPERATURE ERROR
[21.]Why This Error Exists and What it Consists Of.
In adjusting watches to temperature it is not always possible nor expected to obtain a perfect rate between the two extremes, manufacturers generally allowing from two to ten seconds variation according to the grade.
Even when the rate obtained is perfect it will only be so at the two extremes and there will always be a few seconds variation in the middle or normal temperature.
This variation will always be a gain of from two to four seconds in the higher grades of steel brass balances and usually more in cheaper balances.
As there is no possible correction for this irregularity in ordinary balances it has long been known as the middle temperature error and for many years was one of the most perplexing problems that the manufacturer of specially fine timepieces had to deal with.
Various devices were originated from time to time for the purpose of counteracting the error but they were always too infinitely complicated to be of commercial or scientific value, and none of them were ever adopted as a solution of the problem.
In chapter I, No. 3, will be found a description of the distortions of compensation balances in the extremes of temperature and the cause of the middle error is due entirely to the fact that these distortions are not exactly equal in both directions. The free ends of the rims are drawn outward from the concentric form to a slightly greater proportional degree as the temperature decreases from normal and they are not forced inward at an even proportional degree with increase of temperature.
[22.]How Nickel Steel Balances Overcome the Middle Temperature Error.
Through extensive experiment in the foreign laboratories balances containing nickel steel have been found to almost eliminate the middle error, which is reduced to one second or less, making it possible to obtain perfect adjustment in various temperatures.