If you are trying to connect to a microcontroller/microcomputer, you can use a male DB-9 and then use a MAX232 or similar to convert from the +-10V inverted serial that comes out of the cable and convert it to plain 3.3-5V TTL serial
The bottom has two removable plates. One reveals a 9V battery (you can turn this into a portable scale but we think the 9V plug works best) and the other reveals some THM PCB. Not really sure what that's for but perhaps during test they use it?