The H109s drone comes in two flavours; you can see which type of drone you have by looking at the position of the compass. The compass will either be on the front left side of the drone (opposite side to the 5.8Ghz antenna) or the back right of the drone.
You must be aware of which drone you have because the Flight Controller firmware is different on each type of drone. If you inadvertently put the incorrect FC firmware onto your drone the compass will be 180 degrees out. This will cause problems when using the drone in GPS mode.
Hubsan has released little information about this and numerous people have installed the incorrect firmware on to their drone. If you download firmware from the resources section I will always make it clear which version of the drone the firmware is for.
The below drone has the compass on the back right (We will refer to this drone as TYPE ALPHA);
The other type of drone will have the compass on the front left shown in the below image (We will refer to this drone as TYPE BRAVO);