In the video I mentioned that it is necessary to use the calibration function to convert your absolute station pressure to mean sea level pressure. I used the readings from our local Gov't weather station to calculate the offset. However, for those that may not have readings available from a reliable source (I notice a 5 hPa difference between this calculator and our local Environment Canada weather plot), here is a site that not only explains this much better than I did, but also has a free calculator which should enable you to easily calculate your required offset if you do not have a Gov't weather station that is nearby your location: www.wind101.net/sea-level-pressure-advanced/sea-level-pressure-advanced.html
Update, March 2024. Probably worth noting that when we experienced very cold temps (EG: -10C or colder), when the heating element was plugged in, it affected the temperature reading. It seemed that the colder the ambient temp was, the more the reading would be affected especially if wind was not a factor. For example, when the outdoor temp was -30, the Ecowitt would report -25C. Then, within 5 minutes of unplugging the unit, the temp would correct to the actual -30. For our location, ice build up did not seem to be a problem so we did not need the heater unit. If you find you do, I'd recommend the ability to switch it on and off from the comfort of your indoor environment as required, perhaps using a smart switch you can control from your phone.
In the video I mentioned that it is necessary to use the calibration function to convert your absolute station pressure to mean sea level pressure. I used the readings from our local Gov't weather station to calculate the offset. However, for those that may not have readings available from a reliable source (I notice a 5 hPa difference between this calculator and our local Environment Canada weather plot), here is a site that not only explains this much better than I did, but also has a free calculator which should enable you to easily calculate your required offset if you do not have a Gov't weather station that is nearby your location:
www.wind101.net/sea-level-pressure-advanced/sea-level-pressure-advanced.html
Update, March 2024. Probably worth noting that when we experienced very cold temps (EG: -10C or colder), when the heating element was plugged in, it affected the temperature reading. It seemed that the colder the ambient temp was, the more the reading would be affected especially if wind was not a factor. For example, when the outdoor temp was -30, the Ecowitt would report -25C. Then, within 5 minutes of unplugging the unit, the temp would correct to the actual -30. For our location, ice build up did not seem to be a problem so we did not need the heater unit. If you find you do, I'd recommend the ability to switch it on and off from the comfort of your indoor environment as required, perhaps using a smart switch you can control from your phone.