Let $f$ be an entire function then my question is: a formula to find the number of zeros of $f$ on the line $\Re(s)=1,0<\Im(s)<h$ where $h>0$.
I was thinking of applying the argument principle to the rectangle $1-\epsilon\leq \Re(s)\leq 1+\epsilon ,0<\Im(s)<h $ where $\epsilon>0$ is arbitrarily small and $N_\epsilon(h)$ is the number of zeros in the rectangle upto height $h$.
At last we take $\epsilon\to 0^+$.
Is this method correct or any other method please?