Proper usage of "since" and "from" with regard to duration of time

This is an area which often gives difficulty between English and other European languages.

• over a period: "for", "I have been working for two hours" (In some cases you can omit the 'for', eg "I have been waiting two hours")

• from a point: "since": "I have been working since 12"

"From" is unusual here: I think it is only used to give emphasis to the starting point, and notice that it would take a simple past continous, not a perfect continuous: "I was waiting here from 12 o'clock!"

A difficulty that French and German speakers often have is that they want to say "I am here since ... ", which is never idiomatic in English. There is one instance of this that actually does cause confusion some times: when an English speaker asks "How long are you here?" they are asking about the future, but a French or German speaker will often misunderstand that as about the past (i.e. "How long have you been here?").