~20 years ago, HN user sophiebits made a nice arithmetic trainer: https://arithmetic.zetamac.com/ (discussed here: https://news.ycombinator.com/item?id=1728309 The features I plan to add to make it 'complete':. - Source: Hacker News / 2 months ago

You should also find an online arithmetic drill site and set it up to give you 1-digit addition, subtraction, and multiplication problems. You don't have to memorize all the 1-digit number facts (I didn't until I was in college) but boy howdy will it speed you up. You should drill until you can do about 30 in two minutes. I recommend arithmetic.zetamac.com ; you should select addition and multiplication only,... Source: 8 months ago

I've spent time improving my written arithmetic with games like https://arithmetic.zetamac.com/. Speed drills. I still struggle with arithmetic that is prompted without being written down. I.e. If someone said "43+12" I would find this hard whereas doing this on a written online speed drill is fine. Does anyone have any resources that would say outloud basic arithmetic questions and I can then input the answers? Source: 11 months ago

I quite like this for helping cognition but weirdly I can still be good at it but have awful memory at the same time. It's quite addictive just press start. Https://arithmetic.zetamac.com. Source: 12 months ago

Arithmetic game (https://arithmetic.zetamac.com/) is good for testing yourself, and you can change the size of the numbers you're working with if you find you have difficulty with a particular combo. Source: about 1 year ago

I did what you did a few years back. I bought my (1st) Ergodox-EZ and I switched to Colemak and the new keyboard at the same time. I practiced heavily using keybr.com and thetypingcat.com for about 2 weeks, then had to force myself to stop using QWERTY altogether. I just used my EZ for all my typing. This forced me to build up new muscle memory fairly quickly. Once I stopped using QWERTY, my Colemak got alot... Source: about 2 years ago