The Most Common Errors in Undergraduate Mathematics (2009)
Bad handwriting.<p>At age 40 I started taking a masters in stats and had situations where I had exponents on exponents.  This lead me to buy a higher resolution tablet for reading pdf's with tiny math.<p>I also bought a finer point pen and this helped me improve my handwriting <i>a lot</i>.  Closing loops on "o's" or backtracing the upward line of a cursive "t" to not make a loop.  With the finer point, I was able to see my imprecision and improve it.<p>I used to rewrite my finished work in undergrad and now my writing was improved to the point where the first draft was entirely legible.