You can access this form calculator two ways:
When you return to your Focused or Formula Calculator, the last "To Value" will now be in the x register. The last x value can be recalled using the shiift-last x.
Tapping one of the buttons in the "Saved Conversions" will load the conversion calculator with those UOM values.
Tap the save button to the left of the row to save the current conversions.
The "Create Key" button will copy a key to the clipboard the you can paste onto any Focused Calculator. Then you can perform that conversion by tapping a key. See Copy and Paste Keys for details.