fcsuper,
You asked about online checking.
Any time I am asked to check drawings, I require prints. I can work with reduced sized prints, but I prefer full size. I have a highlighter, prefereably blue, and a red pen.
I look at the assembly drawing and parts list, and I work through the fabrication drawings in sequence. Each fabricated detail is compared with its mating part. This means I have the assembly drawing and at least two fabrication drawings open at any time. When the features line up and otherwise work, I highlight all the dimensions and tolerances. If there is a problem, I mark it up with a red pen. If the problem is not simple, I will write a set of accompanying notes.
Once a drawing is covered in blue highlighter, I know it is done.
I go through the drawings in numerical sequence because I want some sort of systematic sequence. It really does not matter what order I find out dimensions are correct in.
On a complex mechanical assembly, I mark global coordinates for all the features on the assembly drawing. This saves a lot of recalculating.
I have seen procedures described more detailed and systematic than this, but this allows me to see every single dimension in the system and form a complete picture of how it operates.
Online checking software supports the red pen functionality, but it does not support the blue highlighter. Also, I have yet to see a CAD system or graphics display that allows you to manipulate three large drawings efficiently on the computer screen. Even if you did have such a thing, it would not be much use unless the drafter had one too, and you had one in the company conference room, and perhaps one on the boss' desk. Yet another one on your shop foreman's desk would enable you to discuss this stuff down in the shop.
Paper works.
Quite a long time ago, I checked a package of drawings, and I advised management that it was a pressure vessel, and that the designer was not qualified to work on it. I have not been asked to check anything since.
JHG