Why does my mains electric digital clock not keep time with the Greenwich Time Signal?

Why does my mains electric digital clock not keep time with the Greenwich Time Signal? Today it is three seconds slow, yesterday it was exactly right, and over a period of weeks it can vary by as much as twenty seconds either way. I vaguely remember hearing sometime that it depends on the frequency of the power supply – is this correct and if so why?
Cec Neale from Norfolk (Age 55+)

How is caffeine removed from de-caff tea and coffee?

How is caffeine removed from de-caff tea and coffee?
D a chambers from West Yorkshire (Age 55+)

What distance would a 747 have to travel before reaching 30000 feet?

What distance would a fully laden 747 heading west from Heathrow on a clear day have to travel (mileage wise) before reaching 30000 feet
Gayle Edmunds from Gloucestershire (Age 45-54)

How do you build a computer?

How do you build a computer? Where can i get a transparent casing?
Tony Phoenix from Kent (Age 5-14)

How can science explain how homoeopathy works?

How can science explain how homoeopathy works? (Note: ‘how’ not ‘if’ if works!)
Hazel Morbey from Lancashire (Age 45-54)

How much land is required per person for sustainability?

What is the minimum area of land required per person of the planet for the sustainability of each? I’m thinking in particular in terms of the land needed for production of an individual’s food and energy.
Howard Eyre from South Yorkshire (Age 55+)

How many stars are there in the universe?

How many stars are there in the universe?
Sean Bunn from Greater London (Age 5-14)
Danny Barry from Middlesbrough (Aged 5-14)
Y3/4B from Swansea (Age: 5-14)

Why are some types of plastic recyclable and others not?

Why are some types of plastic recyclable and others not?
Rosemary Phillips from Surrey (Age 55+)

Could there be a gene for religiosity?

Could there be a gene for religiosity?
Jon Salway from West Yorkshire (Age 45-54)

Is it more economic to leave my central heating on overnight?

I understand that there may not be a definitive answer to this because of the variables involved but, in general, is it more economic (and therefore environmentally friendly) to leave my central heating on overnight and when I go away for the weekend rather than turning it off and letting the house go cold.
Chris Fuller from Hampshire (Age 55+)