You sit at your bench and in front of you is a a function generator and a basic oscilloscope. You connect the function generator to the oscilloscope with a BNC cable and proceed to create a simple signal to measure. Surprise, the amplitude measured on the oscilloscope does not match what you set on the function generator. The sine wave may read 1V peak-to-peak (Vpp) on the function generator, and yet on the oscilloscope, it says 20Vpp or 2Vpp. Now is when you ask,
"What is wrong with my function generator?"