CountDn version 0.21

Minor updates to the CountDn application to improve calculation speed by truncating recursion when adding zero, subtracting zero, multiplying by 1 and dividing by 1. The application is available via !Store.

Actually it takes slightly longer to test for such operations (-0, +0, /1, *1) than it takes to just carry on the recursion so although it then ignores calculations that a user would not regard as distinct (which gives a more appropriate difficulty level discrimination) it takes about 5% longer overall! However 0.14s rather than 0.13s (on Titanium) or roughly double that on a Raspberry Pi, is not likely to be noticeable.