As of Feb 2011, the formula to calculate correct auto fare is:

9*meter-reading + 2

Roughly, this amounts to Rs 11 for the first kilometer, and Rs 9 for each subsequent kilometer.

The meter reading usually shows, approximately, the distance traveled in kilometers. The meter reading also depends upon total time taken, but usually that's negligible unless you were stuck in a major traffic jam, or if you make the rickshaw wait somewhere for a long time.

Between 12-midnight and 5am you're supposed to pay 50% extra ("half return"). However, in my experience, whether a rick driver asks for half return depends upon time of the day and how far out of the center of the city you're going. If you're traveling after 8pm, it is best to check whether he will charge half return or not before getting in.

In case of any problems, you're supposed to sms the place,date,time and the auto registration number to 59994 and the RTA (Regional Transport Authority) is supposed to take care of the problem. I don't know whether this really works, but this is the official line.

As far as I know, none of this applies to PCMC where, apparently, nobody charges by the meter.