It's easy to compare inventory quantities by date using Springboard Retail's reporting tool.
First, go to Reporting >> Analysis and build a report with the following settings:
Select the first date you'd like to see, for example, today. An individual date will work better for this report than a date range.
Set any item or location filters you'd like to include. For instance, you may want to only see on-hand in a particular location or for a certain category of items.
For the most basic version of this report, simply add Item >> Description. You can add any other item groups you want in addition to - or instead of - Description. If you include more than one group and would like to see one result per line, go to the Options tab and unselect "Include subtotals".
The only metric you need is Ending Inventory >> Qty On Hand. This will tell you the on-hand quantities at the close of business for the time period you selected. You could also use Beginning Inventory >> Qty On Hand to see quantities for the beginning of each time period. Current Inventory >> Qty On Hand shows only current inventory and will not show useful results for this report.
This is where you enter the other days or time periods you'd like to see. Choose up to three. For example, to show your on-hands three months and six months ago, just set the appropriate comparison dates.