How It's Measured
I have a circuit (can be assumed as Black Box) I want to measure the input resistance (R2) at DC. I do the common method of using a signal (V1) with a known source resistance (R1) in series with the black box circuit. I look at the voltage across the R2 while changing R1 until it's half of V1. At that point I know R1=R2 and have my resistance under test.
I want to verify R2 by changing R1 to another value and calculating (with an online calculator) the voltage across R2. The problem is, it's far off from what the theoretical value should be. Any ideas what might be happening or further steps to take?