The balance should invariably be true in the round and flat and always in poise before it is placed in the watch.
It is at times pardonable to pass a balance that is not perfectly true in the round, especially when the watch has been repaired on several occasions and it is noted that the rims have a tendency to become set slightly inward or outward after having been perfectly trued. This shows a natural tendency of the metals to find a permanent position which may be slightly away from the true concentric form. A balance of this description may be poised as it is and often will produce better timing results than would be gained by perfect truing and subsequent regulation during readjustment of the metals.
It is advisable to always have the flat true as by doing so any slightly bent pivots will be detected through wavering of the balance and the flat is not very frequently affected by setting of the metals.
Balances should generally be trued and poised in normal or slightly above normal temperature. If they are trued in a low temperature they will be out of true and possibly out of poise in the temperature to which they are mostly subjected. Compensation balances are not presumed to be true in the round under variations of temperature and therefore inspection for true is necessary in somewhere near the same temperature in which they are trued.
In poising balances it is necessary to consider the mean rate of the watch and several details in connection therewith.
If the rate is known to be fast, weight should be added to the light side, and if it is known to be slow weight may be removed from the heavy side.
If the rims of the balance have been trued outward it is a safe rule to remove weight from the heavy side in poising and if they have been bent inward to get the balance true, weight should be added to the light side in poising.
A balance that is in perfect poise can be brought to a perfect stop on a fine jeweled poising tool at any point of its circumference. For ordinary work it is generally considered as satisfactory if it can be brought to a perfect stop at each of the four quarters. When the heavy point seems to be first at one place and then just opposite it is proof that either a pivot is bent or oval in form instead of round.