http://www.flytrex.com/support/flytrex-core-2/manual/
Flytrex Core Mounting
Although Flytrex Core 2 can be mounted anywhere on the aircraft, for optimal altitude and temperature reading we suggest paying attention to the placement of the barometer component.
The barometer component can be located easily - it is placed on the other side of the microSD and it is the only component with a small hole in it. Check out the included picture with marking the barometer, just to be sure.
This small barometer hole needs to be mounted in such a way that prevent direct sun-light from entering it, yet remain open to air flow. This can be very little air and just shouldn't be completely sealed.
Our suggested mounting is to place double-sided 3M or velcro on the other side from the microSD, where the barometer is placed, but without covering the barometer itself. Then, attach it to the multirotor frame so that the barometer is pointing the frame, yet there is a small gap due to the thickness of the 3M/velcro.
Having the barometer pointing to the frame will prevent direct sunlight from entering it, yet the small 3M/velcro gap will allow good air flow to enter. Such mounting will yield optimal altitude and temperature reading