Let Rahim's initial salary be \( S \).
- First, his salary is reduced by 10%, so his reduced salary is:
\[
S' = S - 0.10S = 0.90S
\]
- Then, the reduced salary is increased by 10%, so the new salary is:
\[
S'' = 0.90S + 0.10 \times 0.90S = 0.90S \times 1.10 = 0.99S
\]
Thus, his final salary is 99% of his initial salary, which means there is a 1% loss.
Therefore, the ultimate loss is 1%.