Thanx for the links skimask. Lol, "datasheets", should have thought of that 1 first.

dhouston, i get half of that. Yes i would use 10 bit rather than 8 for more accuracy. I understand "5/1024=0.004882812 or ~4.88mV per bit." but i just want to be clear about the 5. 5 is Vref but what is Vref? I think Vref is the maximum voltage that the PIC will accept on the ADC pin.

In this example the PIC chip's ADC input should range from 0 to 5 in steps of 0.004882812. I think so far this is exactly the same as what i would do if i was using a resistor instead.

Now for the Allegromicro ACS712 chip. +/- i take it means it can accept the current in either way or as AC. Does that make 5A the maximum current rating for this chip?

Vcc/2 makes sense because as far as i know the PIC chip's ADC can only accept a positive number. So a value below Vcc/2 means negative current and a value above Vcc/2 is positive current.

What is the sensitivity? I dont really understand that part