Can you find a website by the battery
manufacturer, or contact them? The equalization voltage can be provided by them, as well as the target specific gravity for each cell. They always suggest taking all the SG readings at the start, then after each attempt at equalization. These readings, with some minor guidance from them will provide you with the measurement of success you need.
Typically, the size of the range of SG between cells tells you when to equalize, and when you've done a good job of it. The target SG and target range varies a little between manufacturer. If you can't get what you want from the manufacturer, surf other manufacturers' websites.