Digital Psychrometer - Handheld Backlight Temperature Humidity Meter Gauge with Dew Point and Wet Bulb Temperature - Battery Included, M350

Under the right circumstances, ventilation can get a house drier than air conditioning, besides being faster and far more energy-efficient. On a warm afternoon, ventilation can dry a house that’s too cool to run the air conditioner. Comparing indoor and outdoor dewpoints will tell you when ventilation will help. That’s why I bought a dewpoint meter in 2014.Nighttime ventilation in summer can be disastrous because as the house cools, the relative humidity will rise. Wood, paper, and some textiles will absorb moisture, and your air conditioner will have to work harder the next afternoon. By displaying RH, a dewpoint meter will tell you when to close the windows.After 3-1/2 years, my old dew-point meter wouldn’t turn on, so I bought a Mengshen. It’s much better. It feels like quality. Off, it draws only 9 microamps; so a battery should last years. On, it draws 2.2 milliamps. By default, it shuts off after 15 minutes. If I never remembered to turn it off, a battery would be good for about 1,000 operations.Trying to spot the old one on a cluttered desk was a nuisance. The new one is bigger and white with a red button. I can’t miss it. Better yet, it has a keyhole slot in back, big enough for an 15-gage nail or a #2 screw. I keep it on the wall by my digital thermometer. That improves accuracy because I can press the button to get a reading without handling it or breathing on it.AccurateIf I give it time, the thermometer agrees well with other thermometers, inside and out.Wet salt in a closed container produces a relative humidity within 1% of 75%. I have a microwave bowl with a vent in the lid slightly larger than the meter shaft. With a little tape around the shaft, it fits snugly. I make sure the bowl is completely dry and cover the bottom with salt. I use a syringe to wet the salt, being careful not to splash the sides or have salty water visible besides the wet salt. Like my last meter, this one reaches equilibrium within 1% of 75%, meaning the temperature and dew point are very accurate under those circumstances.Wunderground has a page showing dew point readings at several locations within 10 miles of me. On days when their readings agree with each other, my Mengshen agrees.SensitiveIf I hold the meter at arm’s length above my desk, the temperature, dew point, and relative humidity will go up and down. That’s because a little of the air I exhale mixes with the currents that hit the sensor.The old one read dewpoints in increments of about 0.6 F. This one shows changes in increments of .01 F. I prefer it.AnnoyancesSlow thermometerThe massive chrome-plated brass shaft was the feature I hated most about the old one. Its thermal mass acted as a heat sink, slowing the response to temperature changes.The Mengshen has a similar shaft that’s even more massive. When I got it, I thought it was defective because it stayed 2 F low compared to my indoor thermometer. Half an hour later, it matched my indoor thermometer. It’s accurate but slow.I left it on the porch until it had cooled 10 F. I brought it in, and it took 45 minutes to warm within a degree of my indoor thermometer. (The emissivity of good electrical tape is much higher than that of polished chrome. A layer of electrical tape on the chrome will speed up the thermometer, but it’s still very slow.)If it’s hanging on the wall, it will give a good RH reading in 10 seconds, but if I take it to an environment at another temperature, I’d better come back in 45 minutes. I do that in unused rooms because a high RH will tell me I’d better give a room AC in summer or heat in winter. If I want to know RH in a hurry, I can use the meter for dewpoint and an infrared thermometer for temperature, then have an online calculator tell me the RH.It was probably designed with a heat sink so that currents of warmer and cooler air wouldn’t cause erratic readings hanging on a wall.C and FBoth instruments let the user cycle through temperature, wet bulb, and dew point. Both mix C and F readings, meaning I must cycle through six readings instead of three. That’s a nuisance. However, if I just want to know RH and dewpoint, I don’t have to switch at all.Wet bulbA wet-bulb reading could be used to check the instrument against a wet-bulb thermometer. It’s calculated from temperature and dew point. It seems the processor was programmed wrong, because the three do not agree. Wet-bulb readings seem to be about 2 F low. The wet-bulb reading in the old one was also off.SwitchingWhen I switch to cycle to the reading I want, sometimes there’s a delay of up to a second, and sometimes I have to hit the button again. Switching off has the same problem. I don’t think the switches are defective. I think during some parts of the update cycle (once a second), the processor isn’t ready.Battery compartment.The battery compartment has no room to spare. It’s tricky to squeeze the connector wires out of the way so the lid will close.I’d say the Mengshen has design flaws, but I still love it.

Accuracy was best in class 5 stars, LCD has light , very nice ! Unit defaults in Celsius however not a deal breaker.....Nice Meter for thy Price.

This is a great tool for checking A/C digital thermostats. I noticed the a/c guy cleaning my system had one, adjusted the thermostat readings with this tool by the ambient temp in the house. For the price very accurate, highly recommend.

I needed this because I travel for work and need to be able to read humidity at sites in side for various reasons. To me it doesn't take that long to calibrate and for what I need it appears to be close enough to tell us an area higher in humidity than another. I am not sure about the % being completely accurate - but it does what I need it to.

Amazingly accurate humidity gauge for about 1/3 the price. I owed this now for a little over 2 months, and I am very pleased with it. I did the salt test (depending on a lot of different factors, it is best to wait 24 to 36 hours to be 100% save. The last thing you want to do is remove your gauge too soon while the humidity is still "at a super-snails pace" increasing) and this gauge showed a 74.50% final reading. In order to get a faster and more accurate temperature reading, I wrapped the metal post with some "self adhering bandage wrap". That is because metal is super temperature sensitive, and takes much longer to readjust or change (say as compared to a plastic post) when being quickly moved into a new setting. I highly recommend this gauge, and I seriously doubt that you will find a better one (I did research for several weeks before choosing) for this low price. I'll finished by saying that I paid the full price, and received nothing in return for writing this review.

4.5 stars because pic shows storage pouch, but its not included. Only meter and battery in package. Not the end of the world, but would of been nice to have a way to keep meter from dust. Other than that…it’s all good.

Humidity is not very accurate and you can’t change the calibration constant. To be honest it does list a fairly wide tolerance, it takes more than a few seconds to make a measurement as the system needs to settle down. I do use it within its capability esp to check temp. Humidity is about 3% off and gets larger depending on value. I’m measuring usually around 45-65% humidity with checks at 80%Thought I would update after 1 yr of use. All measurements are sloowww, temp is still fairly accurate +/- 1F, humidity takes forever, unit will shut off and I’ll restart it-but it’s way off 8+% randomly, 5% other times with no adjustment. This is great features affordable, but for just temp since humidity, wet bulb, dew point etc is garbage.

This is 100% accurate for humidity and temperature readings. I tested this psychrometer with the boveda humidity packets. You wont be able to find another psychrometer this accurate. I highly recommend this psychrometer.

Great products!!!

Execelente producto. Buena sensibilidad, además de que tuve con que comparar (otros instrumentos). Me fue de gran utilidad. Es de fácil manejo.

Éste va dedicado a controlar incubadoras en calibración

abbastanza veloce nel raggiungere e stabilizzare la lettura

The Sensor works fine and performs good. But when it was delivered it came with an empty battery.