How do you apply rogaine foam ?

[aim4hair]

Hey guys,
Sorry if this question been asked before but i would like to know how do you prefer to apply rogaine foam and how to measure the dosage ?
I was using the spray and it was easy to measure, 6-8 puffs and then rub it over nw6 area and im done.. Now im switching to the foam, and i read that if you put it on your hand it melts!! Some ppl put it directly on the scalp but how can you measure the dosage (you might put more or less than the recommended).
Also should i use the recommended dosage to cover nw6 as well ? How can you use the same dosage to cover nw2 and nw6 ?? Is that even possible ?

Your input is really appreciated

Edit: i only use it once aday at night