I clicked and gave it a run, hitting the defaults I was presented with "752 / 8". My mind just lost interest (it is almost 4am mind you) and I closed the tab.

I clicked and gave it a run, hitting the defaults I was presented with "752 / 8". My mind just lost interest (it is almost 4am mind you) and I closed the tab. Then it occurred to me that this arithmetic would be much easier if I had built up to it, i.e. I was used to doing sums like that. So, with that in mind, perhaps you need to offer more? I mean, a lot more. Ways to track my progress as I do build up, ways to give me good places to push the boundaries of my mental arithmetic. I mean, you could go on extending it and making more useful. You could dig out research for the best way to get the user to learn. I'm thinking along the lines of the "goal" to be able to perform sums like those Japanese students who use abacuses to solve massive sums very quickly even once the abacus is removed. There are plenty of interesting features you could add to it! Make people grow from it! I would imagine your target audience would be the younger generation with their parents (schools?) paying their son's education interests. I could imagine every parent seriously considering purchasing if their child was interested.