Voltage Divider
The last five data points from our evaluation with the decade box seem approximately linear. With this I said that we would get approximately linear results for the voltage across the load when it's resistance was half that of the resistor it was put in parallel with. Connection a 500 Ohm resistor as a load and using a 2000 Ohm trimpot (potentiometer) as a voltage divider yielded approximately linear results for voltage which grew rapidly at the high end of voltage across the load.