That feature is new this week.
There are several different standards for measuring the concentration of bleach. Household bleach sold in grocery stores is sold by weight percentage (typically 2% to 8.25%), while liquid chlorine sold by pool stores and cleaning supply stores (typically 10% to 15%) is sold by trade percentage. The two numbers, weight and trade, are fairly close together, but differ just a little because they are based on different historical ways of measuring concentration. I recently updated PoolMath to distinguish between them so it would have better accuracy for higher concentrations of chlorine.