Decimal Places

Does anybody know the decimal place precision between nodes in the compositor?

As far as I know, Blender’s compositing nodes use 32 bit floats for all internal processing. There isn’t any ability to work on lower precision data like in Shake, for example. In terms of actual decimal digits, that will depend on what exactly you are doing, and how you are defining digits of precision “between the nodes”. Generally speaking, a 32 bit float has about 7 decimal digits of precision.