Okay, my puns need work.
So, I'm always sure to keep my easel level, using a level, and I'll often use a long ruler, or my eye to make sure things look right, but when every millimeter counts, and I'm trying to add room on one end of the line for details, and deal with the ramifications on the other end of the line. To be absolutely sure I'm keeping things on the level (get it?) I use one of the oldest tricks in the book: a plumb bob. In my case, it's an old brass gear on a string; the kind you use to tie up your roast.
I have it tacked to the top of the easel, and bring it to the front when I need it. I will then adjust the easel slightly forward. Normally I have it tilted back to keep the canvas on it, but in this case I need the gear to hang freely to let gravity do its thing.
Once it is level, move the canvas to the part you need to check, and tilt the easel back slightly to hold the weight in place. Take mental notes about where you need to adjust your line, and repeat if necessary. You can see that my line veers off to the left as it goes up. So I did some work and checked it again:
Better, but not perfect. I made some more adjustments, and worked on some of the details above the arch. Then I worked on the column details. Here is where it stands now. I haven't checked with the plumb line to see how I did. I had to catch a train and get to my job.
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