Xplorer 1 is the best buy for beginners, with instant live wind speed read out in a choice of Knots, Feet Per Second, Mph or Kph, whilst also displaing the maximum speed recorded when taking your current readings.
Xplorer 2 has a couple of extras than the xplorer 1, with instant live wind speed read out in a choice of Knots, Feet Per Second, Mph or Kph, whilst also displaing the maximum speed recorded, temprature -40 to +80 C and wind chill factor calculation.
Xplorer 3 has - Instant live wind speed read out in a choice of Knots, Feet Per Second, Mph or Kph, whilst also displaing the maximum speed, temprature -40 to +80 C and wind chill factor calculation, Electronic compass displaying degrees
Xplorer 4 is the advanced pocket weather system with a full range of features. It gives instant live wind speed read out in a choice of Knots, Feet Per Second, Mph or Kph, and displays the maximum speed recorded, temprature -40 to +80 C and wind chill factor calculation, Electronic compass displaying degrees, Absolute pressure from 300 to 1100hPa, Relative pressure with calibration, Weather forcast with barometric pressure tendancies and Altitude with calibration: definition 1metre/3feet with a maximum altitude of 8000 metres. You will be hard push to fit any more into this small form factor piece of equipment.