I was thinking, given than h, c and G have different units, I can not compare a unit to other. But when we say that the quantum path integral recovers classical mechanics for very small h, there it seems we have a sense of how small h is. So, h is small... respect to what? Is it respect to E? It can not be, because it has different units. Without G (thus quantum gravity), we can build a linear momentum p=E/c, but again we can not compare it with h. Is it to be compared respective to some angular momentum? Agaist the coupling constant? What if the coupling constant is of order unity, or even a lot bigger than unity? Do we still have quantum mechanics?