Different engines have different scales for their numerical evaluations (for example, Houdini's evaluations are usually much lower than Stockfish's evaluations). This is because different engines use different units in their evaluation functions.
The Fritz 12 instructions manual says:
Chess engines evaluate positions with the help of a numeric value. The evaluation is expressed in pawn units, always from the point of view of White. If the program is displaying a value of +1.30, this means that it considers the white position to be better by the equivalent of 1.3 pawns. If White is actually a pawn up, then the additional 0.3 is the result of positional considerations (mobility, deployment of pieces, king safety, pawn structure, etc.).
This means that Fritz 12 evaluations are calibrated so that +1.00 is equivalent to being 1 Pawn up. (I'm not sure if this is still true for Deep Fritz 14 though...)
Houdini 4 uses calibrated evaluations in which engine scores correlate directly with the win expectancy in the position. A +1.00 pawn advantage gives a 80% chance of winning the game against an equal opponent at blitz time control. At +2.00 the engine will win 95% of the time, and at +3.00 about 99% of the time. If the advantage is +0.50, expect to win nearly 50% of the time.
This means that Houdini 4 evaluations are calibrated so that +1.00 is equivalent to having 80% chance of winning the game.
So I already got the answer to my question for Fritz 12 and Houdini 4. I would like to know the same thing for other engines (for as much engines as possible), preferably strong engines like Stockfish, Komodo, Gull, Critter, Rybka, Hiarcs, Junior, Shredder, etc...