New electro chip...
I think centre line would be too easy. You need a tri-skill anti-rat feature to make it worthwhile. You have an LCD level 3 skill continue and the number reel spinning around. You need a red number, 'e' and WILD on the line to advance one space up the trail. Anything else and you need to pay £10 before you can continue playing. The £10 is a free win for the operator and does not boost the machine's value.
JG