Review on Mengshen Temperature Multi Function Thermometer Hygrometer by Vincent Lott

In some circumstances ventilation can make a house drier than air conditioning, it is also faster and much more energy efficient. On a warm day, ventilation can dry out a home that is too cool to turn on the air conditioning. Comparing indoor and outdoor dew points will tell you when ventilation is helpful. That's why I bought a dew point meter in 2014. Night airing in summer can be disastrous as relative humidity increases as the home cools. Wood, paper and some fabrics absorb moisture and your air conditioner has to work harder the next day. By displaying the relative humidity, the dew point meter tells 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. Thats much better. It feels like quality. When off, it draws only 9 microamps; So the battery should last for years. When switched on, it consumes 2.2 mA. By default, it turns off after 15 minutes. If I never thought of turning it off, the battery would last for about 1000 operations. Trying to find an old one on a crowded table was a nuisance. The new one is bigger and white with a red button. I can't miss it Better yet, there's a keyhole slot on the back big enough for a 15-gauge nail or #2 screw. I hang it on the wall next to the digital thermometer. This improves accuracy as I can press a button to get a reading without touching it or breathing on it. 1% of 75%. I have a microwave bowl with a vent hole in the lid a little over three feet. With a little tape around the shaft it fits snugly. I make sure the bowl is completely dry and sprinkle the bottom with salt. I use a syringe to wet the salt, being careful not to splash the sides or see the salt water next to the wet salt. Like my last meter, this one evens out to 1% of 75%, meaning the temperature and dew point are very accurate under these circumstances. Wunderground has a page with dew point readings from several locations within 10 miles of me. On days they agree, my villa agrees. Sensitive Holding the meter at arm's length from my desk, the temperature, dew point, and relative humidity rise and fall. This is because some of the air I exhale mixes with the currents hitting the sensor. The old one read dew points in about 0.6 F increments. This one shows changes in 0.01 F increments. I prefer it. The electroplated brass stock was the feature I hated most on the old one. Its thermal mass acted as a heat sink, slowing its response to temperature changes. Mengshen has a similar shaft but even more massive. When I received it I thought it was defective because it stayed 2F lower than my room thermometer. Half an hour later it matched my room thermometer. It's accurate but slow. I left it on the porch until it cooled to 10F. I brought it in and it took 45 minutes to warm up to one degree from my room thermometer. (The emissivity of good electrical tape is much higher than that of polished chrome. A layer of electrical tape on chrome will speed up a thermometer reading, but it's still very slow.) Hanging on a wall will provide good relative humidity . read it in 10 seconds but if I take it on a Wednesday with a different temp I'd rather be back in 45 minutes. I do this in unused rooms because the high relative humidity tells me it's better to air-condition the room in summer or heat it in winter. If I want to know the relative humidity quickly, I can use a dew point meter and an infrared thermometer for the temperature, and then the online calculator will tell me the relative humidity. It was likely designed with a heat sink so warmer and colder air currents wouldn't result in erroneous readings hanging on the wall. Both instruments C and F allow the user to toggle between temperature, wet bulb and dew point. They both mix readings C and F, which means I have to cycle through six readings instead of three. This is a nuisance. However, if I just want to know the relative humidity and dew point, I don't need to switch at all. Wet bulb The wet bulb reading can be used to test the instrument with a wet bulb lamp. It is calculated from temperature and dew point. It appears that the processor was programmed incorrectly because the three disagree. The wet bulb reading is about 2 F low. The wet bulb measurements in the old one were also switched off. Switching When I switch to the desired cyclic display, there is sometimes a delay of up to a second, and sometimes I have to press the button again. Same problem when turning off. I don't think the switches are bad. I think during some parts of the update cycle (once per second) the processor is not ready. battery compartment. There is no free space in the battery compartment. Difficult to push the connecting wires to close the cover. I'd say the Mengshen has design flaws, but I still like it.