terminals on my check box

[sham]

i recently bought a check box to check and keep a record of the accuracy of my tester, the check box has two red female terminals at the top of the check box which measures volts ac.

then lower down there are four black female terminal, the first one is marked 10R, the secound 1R, the third COM and the fourth 1M.

next down there is two green female terminal, the first one is marked LOOP, the secound LOOP+5R.

then finally lower down has a three pin socket.

my question is has an one any knowledge of how to perform the checks on the check box and can someone tell me what is the black terminal marked COM.

all help appreciated sham

 

[Spark123]

then lower down there are four black female terminal, the first one is marked 10R, the secound 1R, the third COM and the fourth 1M.

can someone tell me what is the black terminal marked COM.

Common terminal for the resistance terminals?

 

[ban-all-sheds]

Why no instructions?

 

[mapj1]

Bell it out with a meter, but I'd assume it is 1 ohm to com, 1meg to com, etc. and you use these for checking your low and high resistance ranges on your meters.