Erratic reading of voltage, am I doing something wrong?

I want to read resistance on an oscilloscope / plot, so I hooked up a simple setup from a tutorial on reading ohms.

https://create.arduino.cc/projecthub/iasonas-christoulakis/how-to-make-an-arduino-ohm-meter-90fda8

It generally seemed to work, but the numbers were bouncing around. So I looks at the serial plotter and it was hard to tell what was going on.

I'm testing a hall effect pickup on an engine and the output of an ignition box. I hooked up the hall effect pickup in place of the 2nd resistor and it seems to work, but it jumps around too much to be usable. When nothing is near it, it jumps around.

I've heard the DMM (Digital Multi Meters) take an average and that's one of the reasons you can use them for testing certain things like quick spikes.

Some say they get a very, very accurate reading from these, but mine's just bouncing around far too much.

I have it hooked up just like shown in the pic and it did go to the value of the resistor and when I remove the resistor, it instantly spikes, so it is making contact and reading it.

Should I use a 2nd power supply instead of the one directly from the Arduino?

I know that jumpers don't always make good contact, will this smooth if I solder it together?

I want to make a reset, adjustable scale and polling time. Do I need to average the readings? That kinda defeats the purpose of an oscilloscope.

Does anyone know of a better setup that is smoother or more accurate? I see it's working well with one resistor, but still bounces all over.

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