I tried that. It allows to reduze/increase the size along one single axis.

That’s not far away from the usage of the standard move tool of SU.

May be I have to describe a more complex task to explain my issue.

I have a door at a simple furniture. It has, as the first construction step, the same size than the corpus of the furniture.

Now I like to reduce the size of the door (e.g. 50cm x 80cm x 1,8cm) at the left, right, top and above by 0,4cm.
The resulting size should be 49,2cm x 79,2cm x 1,8cm

The standard scale tool from SU offers the perfect “line” for that.
I hold the ALT key (on macOS) and choose the diagonal line inside the door.

Now I can scale exactly in the way I want in one single step.

But I can only enter a proportion (e.g. 0,95;0,95) or absolute measurement (49,2cm;79,2cm)

The task is standard task in the construction of furniture. Many times you need a face joint (I hope that is the correct translation of the german word “Fuge”) for doors.

I’m looking for a tool which allows to enter just “0,4cm” and all is done.

Because the task is “reduce the size equally at all 4 sides by 0,4cm”

Do you have idea how to do that elegantly?

@eneroth3
Yes, it would work with guidelines, but that is not a fast method. I’m looking for a really fast way to solve that standard task.

SketchUp doesn’t do calculations like that through the ‘Measurement’ box. It accepts scale factors and exact values (plus units), not -4 cm for say two out three dimensions.