The software I use in my day job allows for mathematical operations in numerical inputs. It’s a game changer, trust me. We can’t all be rain man
e.g. Want to add 137px to the position of an element located at 1234 px in X.
Simply type 1234+137 in the X position input and bob’s your uncle.
Your parent group is 876px wide and you want to fit 4 equally sized elements inside… no problem type 876/4 in the width of your child group. No need to get out your pen and paper or pocket calculator anymore.