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How to Read Decimal Points of Resistance

Resistors are vital components of electronic equipment, controlling the distribution of current and setting voltage levels. They protect sensitive components and set the amount of amplification given to a signal. With functions like this, it's easy to see why an accurate resistance reading is important. Luckily, common digital multimeters make it easy to measure resistance, as long as you pay close attention when you are taking the reading and understand what the numbers represent.

Things You'll Need

Digital multimeter
Resistor or other circuit element

Instructions

- 1
  Turn off power to the circuit. If the resistor is part of a circuit, the power must be off or the reading will not be accurate.
- 2
  Place the probes across the element to be measured. If this is a resistor by itself, firmly contact one probe to one lead and the other probe to the opposite lead. If you're interested in the circuit, pick two test points and make certain there is good electrical contact between each of the leads and their respective test points. In general, the resistance between two points in the circuit will not be the same as the resistance of the individual components between the points.
- 3
  
  You'll need to note the range setting and the position of the decimal point to interpret the reading accurately.
  
  Set the range of the multimeter just above where you anticipate the resistance to be. It's not critical, but it saves time. You can also use the multimeter's autorange function.
- 4
  Adjust the range for maximum accuracy. If there is a "1." with no other numbers or an "OL" indication, this means the resistance is too high to be measured at the current setting, so click to a higher setting. If there are a couple of leading zeros --- such as 0.013 --- adjust the setting down so as many non-zero digits as possible appear.
- 5
  Identify the position of the decimal point. Values of 1.327, 13.27, and 132.7 can all appear similar, so be vigilant.
- 6
  Find the range of the meter. Some meters will provide a visual indication on the face of the meter; for others, you'll have to look at the dial setting. The settings are usually divided into three ranges, Mohms, kohms, and ohms --- that is, millions of ohms, thousands of ohms, and ohms.
- 7
  Combine the decimal point position with the range to interpret the value. The decimal point will appear at the point that divides integer values of the range from fractional values of the range; that is, in the kohm range a "1" to the left of the decimal point represents one kohm, while a "1" to the right represents one-tenth of a kohm.
- 8
  Recall that each range is one thousand times the next. This means that a value of 386.4 on the kohm scale would correspond to a reading of 0.386 on the Mohm scale. Put another way, the third place to the right of the decimal on the Mohm scale represents a kohm, and the third place to the right on the kohm scale represents an ohm. Places to the right on the ohm scale represent tenths, hundredths, and thousandths of an ohm --- although it's unlikely your meter will be that accurate.

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