Just another Scale Puzzle

I am sure lots of you have already solved different scale puzzles, involving minimum procedures to determine the fake coin, gold piece or some other random object. I recently found another niche of thinking involving scales and I am sure a great pattern can be extracted from there.
Imagine you have an ordinary scale and exactly 4 weights – 1gr, 3gr, 6gr and 9gr.
The question is simple – how many different objects with unknown weight can be measured with the given scale and the given four weights, when you are allowed to put on the scale one unknown object per measurement only?

Publish your answer here - Just Another Scale Puzzle

Solved By: Sergey Sokolov