Sometimes it is convenient to refer to a group of equations by a letter and a number. For example:
2+1 (A1)
2+4 (A2)
x^4 (B3)
x^e (B4)
Placing
\tag{A\theequation}\label{eqn:thisone}\stepcounter{equation}}
instead of just \label{eqn:thisone}
works, but seems hacky (especially manually stepping the counter).
Is there a better way?