animation and line movement

[By Sal]

Hello everyone, and the first time I write here, and I ask for a information on a animation.

Let's say I have a rectangular shape that must move from right to left, I go to Animations and choose the horizontal line and the extension to determine the displacement.



my question is, if I want to determine that the line is 15cm long what I can do to determine the length of the line of movement is of Xcm, rather than lengthen or decrease it manually, which never comes to precision inserting 15cm or 16cm could determine with precision displacement.

There is the possibility of such determination. or code to enter.

A greeting and thanks in advance to those who will give me a feedback.

Hello By Sal (8-D)