ERC is the base of what Poser 8 and up call Dependant Parameters.

It can be some very simple code that you add to the cr2 (figure usually)

This is the code for a new Master dial - normally added to the Body actor.

valueParm Master 1
       {
       name Lower Grips
       initValue 0
       hidden 0
       forceLimits 0
       min 0
       max 1
       trackingScale 0.004
       keys
              {
              static 0
              k 0 0
              }
       interpStyleLocked 0
       }

This is the code for the Ytranslate dial in an existing part .

The lines from valueopdeltaadd  to deltaadddelta are the erc code added to that contol. The new dial has the ytran dial slaved to it. Yoy can have one master to many slaves. The value of the deltaadddelta controls the direction + or - and the rate of change  1:1 1:x etc

translateY yTran
       {
       name Up-Down
       initValue 0
       hidden 0
       forceLimits 1
       min 0
       max 0.465421
       trackingScale 0.001
       keys
              {
              static 0
              k 0 0
              }
       interpStyleLocked 0
       valueOpDeltaAdd
              Figure 1
              BODY:1
              Master 1
       deltaAddDelta 1
       }

 

Here is a good guide http://www.atlantis23.com/erc_download.html

Always work on copies of a cr2 file. If you mess it up you can always delete the copy and start with a new copy.