Value of a middle

[drenx]

I'm trying to learn as much as I can, particularly about scalping, and have recently lucked upon some good middles. I posted the first one I found on the forum, asking the question if it was a good one, and I got pleanty of replies saying that they would have put their whole bankroll on it.

My second one cost me a bit more when it didn't come in, but it still seemed like a good one because of the large middle, although I had no way of knowing exactly how good it was.

On European Basketball, I took:
over 146.5 -115
under 155.5 +107
came in at 157 [img]/images/graemlins/frown.gif[/img]

My question is: is there a formula for working out the value of a middle, or are there too many variables? Anyone know any good references in the area? I've read all the stuff and links in the FAQ, but would like to go further.