Capture a value in Crystal Reports

I have a report that displays warranty item count totals based on month.  The totals change daily as new items are added (open) and existing items are completed (closed).  I would like to capture those values at the end of each month, so that I can see a trend.  Example:  
As of 11:59 PM, January 31st, 2014. the total open warranty items was 58.
As of 11:59 PM, February 28th, 2014. the total open warranty items was 52.
As of 11:59 PM, March 31st, 2014. the total open warranty items was 46.
As of 11:59 PM, April 30th, 2014. the total open warranty items was 38.
etc.

The formula must capture the count of open items and then save that number as a value that I can reference as a static number.  

Thanks in advance for any suggestions.