Dimensions are locked in centimeters?

In anticipation that someone can help me, thank you. Very new to LC. I am  attempting to draw a small house, using Millimeters as the Main Drawing Unit. As an example, I draw a “wall” 1800mm long. To draw the “Wall”  of 1.8 meters, I used 18 points on the worksheet. That is, scaling each DOT on the worksheet as one Centimeter, and therefore each LINE as 1 meter. When I used the Dimension Tool to measure and mark the “Wall” my 1800mm is shows as 18.00. How do I change a setting, so it reads either 1.8m or 1800mm (preferable? After the last two days trying to solve this situation, I am more confused than ever. Printing onto a A4 sheet works fine, but the Dimensions still printed as 1.8m.

If you use mm as unit, everything should be fine with the out of the box standard settings. Don't rely on the dots of the grid, they change their scale dynamically depending on screen zoom level.
Your problem may lie in the dimensions settings, but there are so many possibilities it's hard to tell from what you write. Instead of explaining everything I have made a simple template drawing for mm, scale 1:100 and A4, for LC 2.1.3, with not much changed to standard settings.
mm_1_100_a4.dxf
If you have different needs tell me your specifications and I can make a special version.  

Hi Dellus

Many thanks for the help. It now makes sense, and now working as I wanted.
Thank you very much.