One of the simple experiments for simply observing Hall effect was done. However, I have a problem with the experimental results (attached .xls) First the current in the solenoid was varied while the current in the Hall Probe was constant. Then the current in the Hall Probe was varied while the solenoid current was kept constant. 1.) (Ignore the Helmholz for now)Looking at the left most table. There is a slight negative potential for the low solenoid current values. When the solenoid current was set to 0, and the Hall probe was switched on there was this small negative voltage. There is nothing wrong with the calibration of the voltmeter, as when the current is decreased to 0, the negative potential slowly vanishes. What causes this? 2.) I am trying to identify the mistake made with the Helmholz results. The cables were never switched around at any time. What is going on here? It is possible that we accidentally flipped the Hall Probe over before doing the last Helmholz results, but this would simply result in the Hall Voltages to have a change in sign, not to go in entirely the wrong direction! Please help. Thanks in advance.