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Sorry in advance for the dumb question. I know this is rather trivial but this issue has plagued me for sometime now. Sometimes I have an out of date schematic and will double-check on the board for the value of a resistor. And I can't tell if I have a "1201" or a "1021". Resistors get stuffed upside down all the time. And I can't ohm it because ohm readings all always screwy when you try to measure things in a circuit board. Anyways if there is something obvious I am missing I would love to hear it.

JYelton
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Toasty
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    "Ohm it?" You mean "measure it?" – JYelton Oct 04 '22 at 23:25
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    Usually close inspection with a microscope or jeweler's loupe will show the finer details of the numbers. And in circuit measurement can provide clues, especially if you read both ways to avoid diode junctions. Some meters also have low power ohms measurement limited to 200 mV. – PStechPaul Oct 04 '22 at 23:39

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Without removing the resistor you can measure it in-circuit (both ways) and look at the higher of the two values. Your two possibilities are 1.02K vs. 1.20K. The former is an E96 series so if the highest measured value is more than 1.03K you know it’s 1.2K nominal.

Of course you can always remove and replace it after measurement- that’s typically the only way to determine the value of low-value ceramic capacitors (which are unmarked in most cases).

And usually there are visual cues in the font which allow you to distinguish the orientation, if the part is marked at all (smaller resistors are usually unmarked anyway).

If you still have the marked part reels kicking around there may also be subtle differences in construction and color, particularly if the parts are from different manufacturers.

Spehro Pefhany
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