Run the stock summary by department or maker report.
These reports can provide you with your stock on hand at a date in the past and can be found under Reports>Stock Reports.

a)    Choose the desired location
b)    Enter the date you are after in the date start field.
c)    Leave the date end field as today's date.
 
Go to the totals on the final page of the report. The right hand column represents current stock on hand.
The column on the left under ‘opening stock’ represents what the stock was at the day you entered in the ‘date start’ field in step (b) above.
This figure is arrived at by adding and subtracting stock transactions that have occurred in the date range entered.