Put a coin into the machine which is NOT a pound coin and listen to the noise it makes in the bottom box, it will be a coin landing on a pile of other coins, or into a metal box. Then when you hear the same noise when it IS a pound coin, it is backing.
It is up to you to decide wheather it is worth playing, once I had 6 blasts on a cash stack, expecting £6, got £15 out of the blue. Took it and left. Today played a VIU and had £3 on the nudges, it was backing but not playing well, then one nudge, £10, took it once again.
When a machine is backing £20 is the average to force with, but have more just in case, there is nothing worse than filling a machine for some cu*t to JP/streak! Don't force a dead machine (when someone has taken a sh*t load out!)
There are basic answers for you
