All highest prize watches passing through the Geneva Observatory are equipped with these balances and they have been adopted for commercial use to a large extent by the manufacturers of the finer grades of watches.
From the same source success has recently been attained in applying this metal to hairsprings and using them in connection with uncut balances, but owing to the necessary high cost of production, their general use may be delayed for some years to come. Their general use however would revolutionize the present-day methods of adjusting to temperature as there would be practically no expansion or contraction to deal with.
Nickel steel balances will always be found to have the cuts about one eighth of the circle distant from the arms instead of close to the arms. This is made necessary by the fact that the coefficient of nickel steel is about ten times less than that of ordinary steel, and if the cuts were made close to the arms the brass in expansion would force the free end of the rims to curve inward to such an extent that it would cause an abnormally fast rate in heat.
By making the cuts more central the length of the segments are reduced, thereby causing less curvature of the extreme ends and more nearly equalizing the extent of curvature both ways from the concentric form. This equalization is what causes the reduction in the middle error and its absence in ordinary balances is what causes the larger error.
Non-magnetic or palladium balances are also credited with a smaller middle temperature error than the ordinary steel brass balance, but owing to the unstable nature of the metal they have not proved to be as reliable in other respects and are not used to any large extent.
The middle temperature error is of course a small factor in the larger sense of obtaining time from commercial watches but its influence is apparent in timing and it will therefore be considered further in the section devoted to Final Regulation, Chapter XV, No. 77.