Hi Jeff,
The resin tank holds about 200mL at the Maximum Fill Line printed on the front of the tank. Be sure not to overfill the tank past that line. It will overflow. A 100mL print will be no problem at all. You should be able to print anything under 175mL without thinking about low resin. If the resin does get low, usually the resin will be thinnest on the left side of the tank, closest to the hinge because the tank is tilting to the right. Be aware that even a print slightly less than 200mL could ‘run out of resin’ due to the resin pooling in the right side of the tank.
A nice feature of PreForm is that it will recognize any print that exceeds 200mL and will ask if you would like the print to automatically pause for a refill before the tank runs out of resin, assuming you start with a full tank. You can then safely refill the tank and resume the print, however, you may notice a thin line in your part where the print was paused.
I hope this answers your question.