In Mechanical dimensioning, the dimensions should be staggered so as not to be redundant. This is not as necessary in architectural dimensioning. Dimensions should be spaced 3/8 of an inch away from the object and then 1/2 inch for every dimension out after the first in architectural dimensioning. Mechanical dimensions are equally spaced. the line weights should be about .35 mm, about the same as a 2H pencil. The object itself should have a line weight of about .7 mm, roughly an HB pencil lead width. text should be centered within the dimension unless it overlaps other text. in Mechanical dimensioning, all the text is written in the same orientation. The dimensions are in decimals as well. In architectural dimensioning, text is written according to what view is being dimensioned. Text should be written in feet and inches. A space of 1/8 of an inch should be put between the extension lines and the object, and the extension lines should extend past the dimension lines that same distance. The arrows should be 3/16 x 1/16 and be placed inside unless the text does not allow for them to fit. Architectural dimensioning uses tick marks instead of arrows. Never use dots. They look dumb. Dimensions are shown as such while radius's are indicated with a arrow passing through their center mark toward the dimension. That's about all you need to remember.