Hi blender artists around the world.
I work with architectural visualization in my company with my brother. he works with 3dmax and I work with blender on thing I really want to know how can I produce accurate modeling
for example am modeling a window 1 meter and 20 cm long and 40 cm wide
this can be achieved in 3dmax easily bu till now I don’t know how to do it in blender
thank you for your future help 
Many tools can be used:
used extrude command on a vertex, then if you key 1.2 the line will be 1.2m long. fix the axis with y,x,z
used duplicate command on an edge, then if you fix the axis with y,x,z and key 1.2 the new edge will appear a parallel distance of 1.2m such as offset command of autocad.
Crt+R and you can divide a face. Use duplicate to create a reference and the option Snap to move the cut line to the accurate reference.
visit http://www.blender3darchitect.com/ he has online courses for architectural modeling.
The imperial tab will cause headaches since its in yards. Easy fix is to input .0254 in the scaling box beneath it, now units are in inches. Or select Metric, set scaling box at .01, blender units equal centimeters. And you can input the values you want in units of measure in the operator panel for several functions, as well as in the N panel. and some modifiers.