What is the definition of wind gust? I'm currently building a weather station from scratch. It measures temperature, pressure, humidity, wind speed and direction. The end result shall be a weather station that sends out METAR weather messages so pilots can see live weather in our area.

Now I'm at the point where I'm writing the software and I have only little knowledge about meteorology. More specifically I ask myself when a meteorologist speaks about "gusts". I know it's a wind speed peak, but I'm a bit puzzled how much faster compared to the average wind speed a gust must be to be actually called gust?
I was searching for some definitions, but I didn't really find anything useful.
A US definition is:


  Wind Gust: Is a sudden, brief increase in speed of the wind. According to U.S. weather observing practice, gusts are reported when the peak wind speed reaches at least 16 knots and the variation in wind speed between the peaks and lulls is at least 9 knots. The duration of a gust is usually less than 20 seconds. 


So it must be 9 knots above the non-gust background.