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Post: The problems you are having are most likely being caused by the voltage divider and the inputs are single-ended so they are being measured relative to ground. Ideally, you need a differential ADC input which measures the voltage difference between two points. That way you can measure each side of the resistor and read the voltage across the resistor. The MCP3424 ADC chips used on the ADC Pi Plus are designed to be differential or single-ended inputs but on the ADC Pi Plus, they are configured as single-ended inputs. We do sell a differential version of the ADC Pi Plus called the [url=/p/65/adc-differential-pi]ADC Differential Pi[/url]. It is possible to convert the ADC Pi Plus to differential inputs but it involves removing the input resistors and drilling the PCB. [url=/forums/thread/46/read-resistance-value]This forum post[/url] details someone else who had a similar problem to you and I gave a description of how to modify the ADC Pi Plus to make the inputs differential. The differential inputs on the MCP3424 ADC are only able to read +-2.048V so if the voltage across your resistor is going to exceed that limit you will need to use an operational amplifier to reduce the voltage down to a level below 2.048V.