This is a issue that applies to more things than just the pressure. I have to admit that I'm not quite sure what the manual says but I use the following phrases to make sure it's not misunderstood:
Climb/descend to flightlevel "wun/two/tree/four hundred"
Turn left/right/fly heading "wun/two/tree hundred"
And of course: QNH "wun thousand"
Depending on pronounciation the number zero is easily mistaken for number seven. And I would definitely say that there's a bigger chance you miss a seven in a readback instead of zero (or the other way around) than missing/misunderstanding keywords such as flightlevel, heading or QNH for the number passed.