Use this app to test your working memory and concentration.
Try it before your morning cup off coffee and then 1 hour after to see the changes.
Or if you are using Nootropics, use it to actually test the effects.
By default it goes to 15 number test, but the actual test should be at least 60 numbers. Your ability to concentrate for the full 60 numbers is what is actually being tested, so do not give up early.
NB: This application is ad supported.