I am constructing a signal generator using a kit. Upon soldering it together, I have encountered a problem. The board is marked with two potentiometer slots, identical except for the values named on the board: 50K for the amplitude control and 1K for the offset control. I have two potentiometers, nearly identical. One of them is completely unmarked. The other has B503 etched on the back. How can I tell which one is 50K and which is 1K?