And I find it amazingly inaccurate. I just used it with what I have dived with for many years when using a 3mm suit , an AL 80, and salt water. It said I needed 19 pounds. I have always used 8 pounds under those circumstances because I don't mind being a touch overweighted. This calculator overestimated my weight needs by about 240%.
I have checked out a wide variety of online weight calculators over the years. I find that they generally tell me to use twice what I need.
It works for me.