Reg. dest function in particle tracing module

HI everyone,

This is a very simple question, but since I am a beginner, I couldn't figure it.

Q: dest() function accesses the property of the neighboring particle. I know how dest(qx) works. But what if we have dest(2) or dest (33) and so on. It seems that these numerical values can make significant change in my simulation. I am doing mathematical particle particle interaction with coulomb's force by altering equations using "equation view".

Any suggestion is greatly appreciated..

Thanks in advance..