Beat Block
A device for obviating the necessity of marking the balance to see that it is in beat.
Before taking off the hair spring lay it on the block, turn the balance so the roller pin hits on the side the arrow points, then turn the table so that the line comes under the stud. In replacing the balance put the stud over the line and it will then beat the same as before. By using this tool you also avoid getting the balance out of true.