Count Unique Values Based On Matching Criteria

I have a worksheet with two tabs.

First Tab
Account Name
Account Number

Second Tab
Account Name
Account Number
Account Ship Location Number

On the first sheet each account name and number only appears once.

On the second sheet there may be multiple entries for each Account Name and Number.

On the first tab for each row I want to compare the Account Number column to the Account Number column on the second tab. Where I have a match I need to count how many unique Account Ship Location Numbers correspond.