The digitalPot is a sheet-resistor which is built of diffused p-silicon layer(PAx, PBx) and the internal switches (PWx, which contains some hundred Ohms of resistance when it is on and high impedence when it is off). So, digitalPot is a variable resistor that is right. When we try to measuring resistance between PAx-PBx, PAx-PWx and PBx-PWx of MCP42100 we need to - Applied +2.7V to +5.5V to VDD - VSS to ground - /RS to VDD - keep PAx, PBx and PWx open, no connection with any node of the circuit
Now we can measuring resistance between PAx-PBx, PAx-PWx and PBx-PWx by the multimeter.
Please be noted that the maximum voltage which can be applied to PAx, PBx or PWx should not over the VDD, for example, VDD=3.3V, make sure that the voltage applied to PAx, PBx or PWx equal to or less than 3.3V otherwise may damage the digitalPot.