The next update will add workspaces to the paid version. A workspace is a place where calculations are saved to. Currently the calculator only has one workspace (results history in the calculator), and only the last 20 problems are saved. With the next update, you will be able to create new workspaces and change their size so they can store more results. The first screenshot shows the screen to manage your workspaces. The second one was shown after pressing the "View" button from the first screen.
As you can see, you will be able to export and import workspaces like you can with custom keyboards (first screenshot). When viewing workspaces (second screenshot) you can select problems by clicking on the input. Once an input is selected, you can copy it to another workspace, delete it, or adjust its position in this workspace. To adjust its position in this workspace, simply select "Adjust Position" from the menu and then click where you want to move the selected items to.
If you click on a result while viewing the workspace, the step-by-step screen will be shown for that problem. You can also long-click on any input/result to highlight it for coping it (or part of it) to the clipboard. Finally, if you click on "Settings" you can change the maximum size of the workspace. After the max size is reached, the calculator will delete the oldest item when a new expression is executed.