You need this command while you are creating geometrical rules.
It calculates all macros that were modified in the entire drawing (geometrical rules added, position changed,…)
After you have created or adapted a geometrical rule, the macro will not be automatically recalculated.
This is useful because this way you can recalculate the macros only after a large part or all geometrical rules of an element were created.
If an element was not defined entirely with geometrical rules, then you leave some variables to the computer concerning the placement/size of an element.
It is the current placement of the elements that the computer will try to preserve (as far as possible).
It can however happen that when your elements were not defined entirely and you recalculate, that something unexpected happens with your element (ex. the element is placed some meters further away so that it disappears of your screen).
For this reason it is useful that you decide yourself when the elements should be calculated, and if necessary make the calculation undone with UNDO so that your elements move back to their original place.
We explain this problem what more closely by means of a concrete example:
In this example we have a plate next to a profile.
The profile is fixed (we do not adapt). The plate is flexible (move + adapt).
In this image only one geometrical rule was added and that is the dimension that you see.
In this image the value of the dimension was changed and the macro was recalculated. Because the plate was far from defined we let the computer gamble to find a good solution. In this case the plate was made longer, it is also possible that the plate would be moved.
The solution: better define the plate.
Pay attention that it is also possible that the plate in this example could move in altitude or along the profile. It did not happen in this case because the computer tries to preserve the original placement. This system will not work in every situation the way you expect it to. You cannot count on Parabuild always preserving the correct placement.
This calculation command in combination with one UNDO command is a skilful manner to test your solution while you are placing geometrical rules.
Take care that the elements in your macros were entirely defined!