Rule #10: Be accurate

Unwritten Rule of Engineering #10: Be extremely careful of the accuracy of your statements.

This seems almost trite, and yet many engineers lose the confidence of their superiors and associates by habitually guessing when they do not know the answer to a direct question. … If you are not certain, indicate the exact degree of certainty or approximation upon which your answer is based. A reputation for dependability and reliability can be one of your most valuable assets.