About the weatherconditions @ Ruurlo 

Relative Humidity
The relative humidity is the ratio between absolute humidity and humidity capacity at a given temperature. The meter shows the most recent relative humidity available. Above 90% humidity, the inaccuracy is below 3%. Otherwise, the inaccuracy is below 2%. When available, a grey arrow shows the relative humidity measured an hour ago. The range of the scale is set at 0 to 100%.
Atmospheric pressure
The atmospheric pressure is measured at Ruurlo, a town in the east of Holland and the homebase of Bronkhorst High Tech BV. The value is displayed in hectoPascal and is the most recent value available. The range shown is always 20 hPa, but the scale can vary depending on the current atmospheric pressure.
Pressure history
The pressure history shows what the atmospheric pressure was at certain times during the last 24 hours, all relative to the current pressure. At the time of the screenshot, the atmospheric pressure 12 hours ago was 6 hPa/mbar higher than it is now. The less steady the pressure values are, the more likely it is the weather is changing. The scale ranges from -10 hPa to +10 hPa.
The windspeed is measured every 10 seconds, this meter shows the moving average over 10 minutes. To measure the windspeed and direction, a temperature sensitive element is used without any moving parts. It has an inaccuracy below 3% and handles speeds up to 25 meters per second. The windspeed on the very common scale of Beaufort is given also. When available, a grey arrow shows the windspeed measured an hour ago. The scale can vary depending on the current windspeed.
The winddirection shown is a moving average over 10 minutes. The yellow triangle points to the direction from where the wind is coming from. In the screenshot, an east-southeast wind is blowing.
The precipitation meter displays the percent of time precipitation was measured during the last 10 minutes. It's very sensitive and can easily show precipitation that is less than the minimum shown in the quantity meter. The range of the scale is always 0 to 100%.
Precipitation quantity
The precipitation quantity shows the number of milimeters precipitation that has been measured during the current day. The precipitation quantity has an accuracy of 0.2 mm. The scale can vary depending on the total precipitation measured.
Precipitation history
The precipitation history shows how much precipitation has been measured during the last hours. The history goes back up to 8 hours. At the screenshot, you can see that 0.4mm precipitation has been measured 2 hours ago. The scale can vary depending on the precipitation measured during the last 10 minutes, but the smallest step is never less then 0.2 mm.
The temperature is the most actual value available and has an accuracy of +-0.2 degrees Celcius and ranges from -40 up to +60 degrees Celcius. To convert degrees Celcius to degrees Fahrenheit, use the following formula: F = (9/5) * C + 32 (25 degrees Celcus for example, is 77 degrees Fahrenheit). The range shown is always 20 degrees, but the scale can vary depending on the current temperature.
Time and date
All values shown where measured and/or calculated at the date (dd-mm-yyyy) and time shown.
Windchill Factor (low temperatures) and Heat Index (high temperatures)
The windcill factor and heat index are calculated using formulas also used by The National Weather Service (US). The windchill factor tells the cumulative temperature effects of the air temperature and the velocity of the wind. It is the temperature that a person feels because of the wind. For example, when it's around freezing temperature outside and the and the wind is blowing at 15 meters per second, the windchill factor causes it to feel like it is about 8 degrees below zero. In other words, your body loses heat as though it is -8 degrees outside. The Wind Chill factor is only available when the calculated value is lower than the actual temperature.
The heat index takes the current temperature and humidity into account and calculates what the temperature would be if the air were at 25-percent humidity or so (very dry). It's based on the fact a human body needs to get rid of excess heat. Up to about 24 degrees Celcius (80 degrees Fahrenheit), it's easy to dump excess heat simply through radiation. Above this temperature, your body does not have enough surface area to get rid of the heat fast enough, so your body turns on your sweat glands to make evaporative cooling possible. Evaporative cooling works great if the air is dry. In high humidity, however, it doesn't work very well -- the sweat cannot evaporate because the air is already saturated with humidity. On this scale, high humidity can make you excruciatingly hot because your body has no way to eliminate excess heat. The Heat Index is only available when the temperature is above 18.3 degrees celcius.

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