I haven't seen that one before. I usually liked this one:
bmijs.is.tuebingen.mpg.de/en/body_masses/get_data (there's a female version too)
You probably want to keep the exercise number at 1 or 2 (just normal walking around, carry stuff from errands, work tasks, etc.). I do like how you can also adjust inseam, since it may be slightly off.
If you set and lock one slider, the rest of the unlocked sliders will move automatically. In addition to height and weight, it might also mean guessing something like.. how much to gain until your waist or ass is a certain size.