Match two columns and count the third column's value

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.

apply this formula in M3

=COUNTIFS(Sheet1!$B$2:$B$1916,'TRACK YARN P.O. WISE'!H3,Sheet1!$C$2:$C$1916,'TRACK YARN P.O. WISE'!I3)

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first of all thanks for replying. this formula is counting a single product used how many times which i don't ask for. i want only how many products were used in p.o. number 3840 B. and the correct answer is 3. while this formula is showing how many times a single product 2/5 cotton was used.

use this formula, result will be 3

=SUMPRODUCT(((Sheet1!$B$2:$B$1925='TRACK YARN P.O. WISE'!H3))/COUNTIFS(Sheet1!$B$2:$B$1925,Sheet1!$B$2:$B$1925&"",Sheet1!$C$2:$C$1925,Sheet1!$C$2:$C$1925&""))

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yeah absolutely done. thanks a lot from the bottom of my heart. you are very responsive and intelligent also. i always mess with where the brackets will start where to put comma, semi colon, double quotes. these types of things always bother me. is there any course of language or book. i would like to have some suggestion. and again thanks a lot for the formula.