...with a very polite email memo describing the correct procedure for calculating percentages and concluding "It would be helpful for future calculations of this character to be undertaken according to the approach I have outlined above." It might give offense (I hope it does), but I took some care in crafting it in a studiedly neutral tone employing not a single word or phrase that would prove toxic should I be obliged to consume any part.

cordially,

(Edit: repit; consonant substitution)