Match two columns and count the third column's value

[akshay6s]

HI,
in sheet 1 there are 3 main columns B,C,D. column b is purchase order number and column c is product description and column D is quantity.

in the second sheet in cell M3, i want the unique number of product used from sheet 1. in cell L3 i have counted that but this is the result from second sheet. while i want to cross check the results. that's why i want the how many type of product used in any particular p.o.

for example:- in sheet 1, if we select the p.o. no. 3840 B it shows the result in c column which is total 17 if we count them, but i don't have to count them again and again. i want to know only how many type of product were used that is 3. so i want the result in m3=3 . p.o. no. should be follow by cell h3. as p.o. no. changed in h3 result should be according to that. and h3 controls by B1.

ins short, in second sheet as we enter any p.o. number in B1. it shows automatically in h3 and i want how many type of product were used in h3.