I grasp new concepts pretty easily when it comes to math and science, but I constantly make small errors in arithmetic or forget to carry signs and symbols when working by hand.
Can anyone relate to this?
My hypothesis is that the ADHD brain is good at abstraction and creative thinking but struggles with linear implementation.
I can totally relate to this! I thought I was hopeless at maths at high school. Now I have a graduate degree in machine learning, statistics and data compression. I have an excellent grasp of advanced concepts like abstract algebra and information theory, even though I struggle to make change.
Yes can relate- sounds like you have the inattentive type - miss these things - like when I was in school ( I am 75) everything was done by hand or on a typewriter. I am a great writer but I cannot spell for the life of me! And, when I worte stuff in I had to go back over it because i never crossed my t's or dotted my I's so year I can relate!. In fact when I was in Grad school my friends got me something called the bad spellers dictionary - words were listed like most bad spellers would write them- I still have it and think- yes that is the way I spell. I am also great in science but lousy in math. so part of the inattentive ADHD brain
It happens to me all the time!!!! I am doing a phD in physics and I usually understand the concepts pretty well but I have a lot of tiny errors (like forget a minus sign xD) that change completly the results!!! I usually have to review my codes or mathematical expressions, so my trick for that ( horrible task ) is use something visual to track where I am, I mean, on the computer I use the cursor to resalt what I already read or analogic I use a pencil to follow the mathematical description and make tiny marks (that can be erased later) when I am sure that are well... So, I suggest you to explore what works better for you, and don't let the frustration make you think that you cannot do it 😉
Medication is good but adding to your toolbox while on medication is best! 
Is it bad to ask for a stimulant?
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