Place it at the end of a counting sequence or reveal, after the total lands. Build the moment with sudden suspense before the figure appears, then follow a wrong total with the wrong answer gameshow sound for a second beat.
About this sound
A short spoken clip, about three seconds long, where a voice delivers the line 'You would have to use a calculator' in a flat, matter-of-fact way. It gives a dry, amused feeling, like calling out a number so large or a sum so messy that mental maths is pointless and everyone knows it.