The Kestrel Elite Weather Meter with Applied Ballistics which has been referred to as the Kestrel 5700 Elite, is an updated version from the Discontinued Kestrel 4500 Applied Ballistics Meter in November of 2015. That being said... functionally, you're not getting more environmental or ballistic features. So don't feel the need to upgrade unless you find the other exciting changes necessary.
What's new with the Kestrel Elite Weather Meter with Applied Ballistics over the previous Kestrel 4500 Applied Ballistics series : Bluetooth LINK to Smartphones / Mobiel / Android / IOS
Takes 1 AA battery (instead of 2 AAA)
Battery door is in the back, sealed away from the motherboard, should your battery leak as was common with all the 4000 series
Improved high resolution screen for any lighting (even sunlight) and easy on your eyes.
