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Please excuse what is probably a very simple question. I don't know the correct terminology to describe this better than "added here" as these don't appear to be "in parallel" or "in series" since they're floating off to the side.

enter image description here

Here I am measuring a 100K resistor and it shows as ~100K on the multimeter.

But when I connect the resistors up like this then the resistance changes. I haven't moved my multimeter test points.

enter image description here

I've drawn these out and simulated them using Circuit Wizard.

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  • \$\begingroup\$ That's because you're putting additional resistors in series with the bottom resistor. \$\endgroup\$ – Hearth Oct 15 '18 at 13:14
  • \$\begingroup\$ But my multimeter test points are only connected between the one 100K resistor. \$\endgroup\$ – Zhro Oct 15 '18 at 13:16
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    \$\begingroup\$ You should study a little bit more elemetary circuits,... \$\endgroup\$ – Marko Buršič Oct 15 '18 at 13:21
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    \$\begingroup\$ @Zhro Not so: in the bottom left circuit, you have two 100K resistors in parallel, and in the bottom right circuit you have a 100K resistor in parallel with a 300K resistor (three series 100K resistors). \$\endgroup\$ – Hearth Oct 15 '18 at 13:22
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    \$\begingroup\$ "Off to the side" doesn't matter. "Parallel" and "series" refer to paths of current flow, not the position of the parts. \$\endgroup\$ – JRE Oct 15 '18 at 13:25
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In the first case you're measuring this (TP1 and TP2 are your test probes):

schematic

simulate this circuit – Schematic created using CircuitLab

Which is equivalent to 50kOhm

In the second wiring you're measuring this:

schematic

simulate this circuit

Which is equivalent to 75kOhm

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  • \$\begingroup\$ Can you expand this question on why it isn't measuring only between the points of least resistance? \$\endgroup\$ – Zhro Oct 15 '18 at 22:53
  • \$\begingroup\$ Zhro, I think you need to understand basic concepts of voltage, current and the ohm law. The ohm-meter will apply a known voltage accross test probes and measure the current. current will flow through both resistors R1 and R2 in first example, and R1 on one side and R3, R3 and R4 in the second. PS: You can imagine that they are pipes an water flows through them. Smaller resistance means more flow, but if you parallel pipes, the resulting flow is added. But you really need to study some basics. \$\endgroup\$ – Undertalk Oct 15 '18 at 23:54
  • \$\begingroup\$ There is a common, but very misleading, statement that "the current flows in the path of least resistance". While this statement is true, it is incomplete - current flows in all possible paths. The path with the least resistance will carry more current than any other path, but the higher resistance paths also carry current. A multimeter measures the effective resistance between its probes, which is rarely just the resistance of the component between the probes, if the component is in a circuit. \$\endgroup\$ – Peter Bennett Oct 16 '18 at 1:19

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