I am currently attempting to take a 4 wire measurement sourcing current with a Keithley 2400. However I keep having very erratic measurements. I am currently measuring a 150.5nm Silver thin film. I am worried that the impedance of the device may not be high enough because I keep reaching compliance or the current is leaking out of the probes. When it is in the 2 wire mode the program produces expected values, but in the 4 wire it is difficult to obtain a steady reading. Please help.