After a particularly lengthy shop queue, I started to consider the job of a cashier. Although electronic tills have reduced the manual adding needed, they possess a particularly good grasp of it when needed. So quick as to be easily beyond what I would manage.
This led me to thinking of what I could learn to do. Not necessarily something incredible but merely, say, multiplying two 3-digit numbers instantly (eg: 452 × 987). So the question I faced now was how best to practice towards that. The result is SumImprovement: a rapid-fire maths practicer.
For as long as I can remember adding 2-digit numbers and multiplying low 2-digit numbers has been largely automatic for me. Not necessarily instant but quick to the point where I do it without conscious thought or difficulty. This is the sort of thing I want for 3-digit numbers.
It's useful. Anyone looking to develop their mental arithmetic from young children to people like me could find it handy. Adding other types of questions (calculus, matrices, even statistics) could make it even better. In the meantime, here goes an experiment in what I can make myself do. I'll post back with progress as time passes.
 Even in adding 2-digit numbers there's some quirks: when the least-significant digit wraps around in certain ways my unconscious process can stall slightly. As such the ability to practice addition as well was born.
 A recent aim of mine has been personal hack nights on Tuesdays - a day when I've plenty of free time and usually got some good sleep the night before. SumImprovement is the major product of a couple of them.