Used Signatone PRO4-4000 Four Point Probe Resistivity Measuring SystemSignatone PRO4 4000 Four Point Probe Resistivity Measuring System The Signatone Pro4 is a manual sheet and bulk resistivity measurement system designed for testing semiconductor materials, metal depositions, and conductive coatings. It utilizes a four point inline probe head to apply an electrical current and measure voltage drop, calculating accurate resistivity without destructive sample preparation. Unit includes the Keithley 2400 Source Meter.