Dec 2, 2014 in Industrial Surveying by

Level versus flatness – Often these two terms are used concurrently in conversations around machine alignment leading to misunderstanding in the expectations of the process.

There is an interesting article on The Alignment Blog where the terms are well defined.

In summary  : Level simply means that the machine or surface  is parallel to earth, or horizontal. Flat means that all points on a surface are in the same plane ( within the tolerances specified) .

Traditionally the horizontal plane and vertical planes had to be used as the reference planes against which flatness could be measured using instrumentation such as machinist levels, levels and opto-mechanical compensation instruments.

Today however with laser trackers and software such as polyworks for three dimensional coordinate transformations one can utilise non gravity defined surfaces as the machine orientation surface.

http://thealignmentblog.com/blog/2012/10/15/defining-level-vs-flat/