I'm a little disturbed that they are using this as evidence, yet one of the "forensic scientists" is quoted as saying
Normally this frequency, known as the mains frequency,
is about 50Hz," explains Dr Alan Cooper
That is incorrect. Normally it is exactly 50Hz. That's why the time displayed on battery-powered clocks drift over time, but clocks plugged into the wall stay correct.
It is not very exact. The total phase error can be hundreds of cycles.
In the synchronous grid of Continental Europe, the deviation between network phase time and UTC (based on International Atomic Time) is calculated at 08:00 each day in a control center in Switzerland. The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60 sec × 60 min × 24 hours = 4,320,000 cycles per day.[21] In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half hour.
