When you want to add or subtract to an existing figure, you must do it in reverse
So say you chair has a base height (bottom offset) of 600mm and you want to make it 870mm.
Select the chair (or all chairs with the same height).
You will see the figure of 600, select (highlight it).
Now type 270 + and ENTER.
270 will be added to the 600.
This works for addition and subtraction, but not multiplication or division.
Otherwise you have the multiply with vertical offset if you want to start from one object and distribute it.
There are align and distribute tools that all can help to alter the positions across a range of existing objects, but unfortunately this does not work for heights (z axis).
Or of course you can simply select and drag in elevation / 3D from one node (base of chair) to another node (top of step) while constraining vertically with the SHIFT key.
Then there is no need to type any figures.
One of the forum moderators.
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