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Wagner MMC220 Moisture Meter
Our Score:

As with all pin meters, it can be very difficult to insert the pins far enough into hardwoods to obtain accurate readings. Attempting to do so often results in bent or broken pins. Also, short pins will not reach far enough towards the center of thicker slabs where higher moisture is found. According to the United States Department of Agriculture, boards should be read at a depth of one-fourth to one-fifth of its thickness.

The Delmhorst RDM-3 is a pin-style meter that can be used for measuring moisture in wood. It is not designed for measuring moisture in other building materials. Its rugged build should stand up well to a lot of use. Its intuitive navigational keypad makes it easy to use with minimal reliance on the manual. It offers features that most other meters do not, including data storage and the ability to download data to a computer. Accuracy test results indicate that this meter has some limits, especially when MC falls below 8% MC.

The Delmhorst RDM-3’s reasonable accuracy (except below 8% MC), its many features, such as data storage capability, and its sturdy construction all make it a reasonable choice for many applications, especially where a pin-style meter is preferred


  • Adjustable alarm to alert the user when a preselected MC is reached.
  • Several external electrode accessories are available.
  • Stores up to 1,416 readings and offers computer download of data.
  • Solid construction; suitable for rugged use.


  • Some issues with accuracy, especially below 8%.
  • No built-in calibration check.
  • Surface moisture has a significant effect on readings.


Objective Evaluation – Overall Score 3.6 out of 5.0

Delmhorst RDM3 Objective Test Summary

Accuracy – 3.9 out of 5.0

This meter provided reasonable accuracy, although readings for the ponderosa pine samples tended to be consistently low above about 20% MC when compared to ASTM D4442 oven-dry standards. In addition, below about 8% MC, the meter’s readings tended to be consistently high for all three wood species (Douglas fir, ponderosa pine, and hickory) when compared to ASTM D4442 oven-dry standards.

Delmhorst RDM3 Accuracy Chart

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Surface Moisture – 1.0 out of 5.0

Surface moisture had a very significant effect (about 12% MC) on this meter’s readings.

Delmhorst RDM3 Surface Moisture Chart

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Meter Temperature Test – 4.5 out of 5.0

Meter temperature had a relatively minor effect on this meter’s readings at both low MC and high MC. The most significant effect was with a low meter temperature of 34.8° in the presence of high MC, which decreased the reading by about 1.6% MC compared to the room temperature reading. Otherwise, meter temperature affected the reading by 1.0% MC or less.

Demlhorst RDM3 Meter Temperature Effect on Meter Readings Chart

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Wood Temperature Test – 3.5 out of 5.0

Wood temperature had an effect on this meter’s readings. This was especially the case at high MC. At a low wood temperature of 34.8° F in the presence of high MC, the reading increased about 3% MC compared to the room temperature reading. At a high wood temperature of 110° F In the presence of high MC, the reading decreased by about 2% MC.

Delmhorst RDM3 Wood Temperature Effect on Meter Readings

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Reading Repeatability – 4.0 out of 5.0

The readings of this meter were not entirely repeatable, showing a minor tendency to vary.

Delmhorst RDM3 Reading Repeatability

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Drift Test – 4.0 out of 5.0

Readings for this meter showed little tendency to drift after 3 seconds.

Delmhorst RDM3 Meter Reading Drift after 3 Seconds

Cable Interference – N/A

The cable interference test was not performed because no cable accessories are available for this meter.

Delmhorst RDM Effect of the Cable Interference on Meter Readings

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Subjective Evaluation – Overall Score 4.2 out of 5.0

Subjective test summary results for the Delmhorst RDM3 moisture meter, earning a subjective score of 84%

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Ease of Use – 4.1 out of 5.0

This meter features a five-button navigational keypad that requires very little use of the manual for gaining familiarity with its use. The manual itself provides reasonable documentation for resolving issues while using the RDM-3.

Quality – 4.3 out of 5.0

Sturdy, durable construction. The meter itself is unlikely to break or malfunction with normal use.

Comfort – 4.0 out of 5.0

This meter offers an ergonomically-designed shape that fits reasonably well in one’s hand. It is not compact enough to fit easily into a shirt pocket, but it does come with a sturdy plastic case to protect the meter when transporting it from one job site to the next.

Versatility – 3.0 out of 5.0

This is a single-mode meter (pin mode only) that can be used with external electrode accessories if desired. The RDM-3 is not capable of giving relative readings in non-wood building materials.

Range – 5.0 out of 5.0

The RDM-3 reads from 5% to 60% MC. However, it is worth noting that measurements taken at moisture levels below about 8% MC tend not to be as accurate.

Features – 4.6 out of 5.0

The RDM-3 is a feature-rich meter capable of storing up to 1,416 readings. Stored data can be downloaded to a computer. The meter also features an adjustable alarm that alerts the user when a preselected moisture level is reached.

Customer Service – 4.5 out of 5.0

Delmhorst’s customer service was knowledgeable, helpful and polite. The representative was able to answer all the basic questions about repairs, returns, etc. Fast response to both telephone and email inquiries. Manual available online.


Warranty and Repair Information:

  • One-year warranty on all Delmhorst meters, and a 90-day warranty for optional electrodes.
  • The meter must be physically inspected before the actual repair cost can be determined.
  • 3-5 business day turnaround on repairs.

Our review is based on Moisture Meter Experts independent evaluation of the meter, which was purchased by Moisture Meter Experts or provided free of charge by the manufacturer. By purchasing this meter through the links above, Moisture Meter Experts may be compensated either by your purchase directly from Moisture Meter Experts or from commissions from an affiliate. View our Review Procedures section to learn more about our proprietary evaluation procedure and expertise in the field of moisture meters.