Question about the grid

Hi everybody

I was reading in Blender 3d : Noob to pro - Page: The Buttons Window
http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro/Blender_Windowing_System
And there is one thing i didnt understand in it :
" The grid lines represent one Blender Unit (BU). How big is a BU? It can be however large you would like it to be! A BU could be an inch, a centimeter, a mile, or a cubit. A BU lets you decide the scale. "
Will you explane a little more about Bu .

Easy. You decide What a Bu is ( a meter, or centimeter, or kilometer, or foot, mile…). For example, if you decide that one Bu must be one meter, then five Bu are five meters.

If you open the Transform Properties tab with N and change LocX:0.00 to LocX1.00 then your Active Object has moved 1 BU along the +X axis. Now, if you want to build a wall 10 meters long and 5 meters high you can make each BU a Meter and the wall will stretch from X:0.00 to +X10.00 and from Y0.00 to +Y:5.00. From that you can work out (on paper) the exact size in BU’s of the door and windows.

%<

Thanks for clearing this to me

am I wrong, or does the smallest gridsize corresponds to 0.01 BU???

Using n, you can enter in a location down to the .0001 BU, though its most useful at .001 BU (In meters that would be 1 millimeter).