RecipeCalc doesn't have a recipe for the calculator. In single player mode, you simply have to turn on cheats and get one from the "Tools" creative tab. If you are playing in a server, ask your administrator.
If you are the author of a mod pack, you can add a custom recipe by yourself using other mods like MineTweaker
When holding in hand, right-click to open the GUI. In 1.12.2 version you can open the GUI in either off-hand or main-hand. In 1.7.10, of course, you can only open it from the main-hand (because there is no off-hand)