To determine the number of teeth on the belt required you will have to know four bits of information:

1. Number of teeth on the vacuum pump pulley.
2. Number of teeth on the crankshaft/drive pulley.
3. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as close to the crankshaft/drive shaft center as the slot will allow.
4. The center distance between the vacuum pump shaft and the crankshaft with the pump slid or rotated as far away from the crankshaft/drive shaft center as the slot will allow.

Once you have these bits of information and entered them in the calculator there will be 3 outputs:

1. The minimum number of teeth on the belt.
2. The maximum number of teeth on the belt.
3. The Center of Adjustment. Which is the average of these two numbers.

The Center of Adjustment should place the pump in a position where the belt can be tensioned or removed without bottoming out the bolts in the bracket slots. Use the number of teeth displayed in the Center of Adjustment to search for a matching belt. There are a limited number of belt lengths/teeth available. The number of teeth in the Center of Adjustment may not be available, in this case you will have to go up or down one tooth to find the belt available.