CAD tip # 12624:

So e.g. the length of a drawn wall segment can be specified not only by entering e.g. 4000 (mm) but you can enter e.g. the value of 4m or 0.004km or type 6'5" or 20in or 2.5ft or 10yd, or you can use an arithmetic expression to enter the length or angle dimensions (prefix them with the equal sign), e.g. =4000*75% or =4000/3 or even a combination of units, like =5000-7'6".