Last April, DoT fixed the frequency of PCO machines at 16 kilohertz to eliminate overcharging. It also started regular monitoring of PCO meters in the exchanges. ``Pulse jumping is not possible anymore,'' asserts local DoT Vigilance Officer S N Rahul.

But pulse jumping or no pulse jumping, Rahul's own department has been regularly receiving complaints of overcharging. What's more, they have found many of them true and actually cancelled connections. All this while everything was well at the DoT end: the meters of offending PCOs kept operating on the DoT-assigned frequency.

A DoT official admitted that the new technique had only reduced meter tampering, not eliminated it. In the last one month, about 15 PCOs were raided on the basis of consumers' complaints and the connections of three cancelled; two others were let-off with a warning. Earlier, there had been many more cancellations, he said.

Interestingly, the official admitted that cancellations were no indicator of the extent of malpratices. Many consumers are not even aware that they are being over-charged, and the PCO equipment could be tampered with; and even those who could have a suspicion often don't know what is the remedy.

A dealer of PCO equipment, who doesn't want to be identified, said, ``Tampering with PCO equipment has become more risky and complex, but it can be done nevertheless.'' And it can be done according to the demand of the PCO operator. The easiest of the manipulations ensures that ``the meter jumps by one unit as soon as a customer keeps the receiver down''. This is safe and fool-proof, he assured.

With some expertise, meters can be made to jump more. For example, the Mumbai pulse can be reduced from 5 to 4, inflating the bills of unsuspecting customers by 20 per cent. It is done by manipulating the data base of the machines, said the dealer.

A DoT official said they could identify tampering of machines by just a look at the print-out of the bill. So, next time you suspect a PCO has overcharged you, you know where to take the print-out.