I would guess that the values in that column with no -ve or +ve can be taken as positive. Since the dome or dish/reliefs modify the crown, I think we can safely say by now that if it's adding to the crown volume it's a positive value and taking away volume then it will be negative. These values are used in the formula for working out the CR, so I assume (without knowing for sure) that there might be a value allocated as a constant for a totally flat top piston that is perfectly level with the deck.
