It works on my iPhone.
I'll have to try it on my iPad later. I don't have it with me right now.
It won't spit out a number unless you have all the input fields (Grain Temp, Grain Weight, Water Ratio, and Target Temp) populated.
I double checked that I did, but I'll check again. The results don't appear on some other page, do they?
OK, I have grain temp at 71, grain weight at 13.75 lb., ratio at 1.6 and target temp at 148. When I hit the calculate button nothing happens except that the button turns blue for a second to indicate I've pressed it.