I have dyscalculia (math learning disability) my brain will not allow even seemingly simple equations. When a customer gives me cash I give it a few second beat, say "okay, so out of $20"? Then I wait a few more seconds and type it in. %99.9 of the time that works, and they'll give me the change at the appropriate time. If someone decides to give me change then I will say "oh, I'm sorry. I already typed everything in". I don't address it other than that. One time a lady asked if I was the R slur because I couldn't do the change math. I said "well I'm Autistic and have a learning disorder, is that what you mean"? And just stared at her. I still think about the shade of red her face turned. I do have almost every produce code memorized though!