There is a new Experimental Manual Calculator that can be found under the General Settings. Like the Manual Calculator it does not take into account how splitters and mergers prefer to split/merge in game. So priority splitters/mergers are still useless as is the preference of normal splits/merges to be as even as possible. Also like the old version, this should always run quickly. However unlike the old Manual Calculator where the entered number defined the value, the experimental one uses the inputs as limit, like the Full Calculator. This means that you can no longer get numbers greater than what you entered if you enter too much and you can no longer get negative numbers.
This should be a strict improvement over the old Manual Calculator and should eventually completely replace it. Let me know if you have any issues with it and also let me know if you are using it without issue. Links to file bug reports and links to the discord can be found in app in the about section.