Follow one concentric ring across the (support, panel, canvas). This and visually marking the left and right sides of the image should give you your final painting image width.

If your painting for more then one day on location, mark everything about your easels position. 
When going after accuracy not speed everything must stay in the same relative position.

I've given up on trying to catch the sun so I'm spreading the cool around with a glaze of Cyan..

I considered it 100% covered by 3:00. 
I still haven't got the shape of the main tree yet but I will right after this break.

I would say there are 30% more flowers today. Soon the petals will blow on the hi-way, I'll have to be here at 6:00 in the morning to catch that. The day after tomorrow I hope. 

4:48 finished for the day, ten to five, I thought I was out of that rut.. It was a perfect day, and it just happened to be my 61st birthday!

It's 10:57 and the sun has gone for the day. Perfect timing, I got all my correction work done in the paintings with the 4:00 colors by using the same colors that were already down. Now the colors are here and I can go forward.
1:17, Got to take a break, the suns back out again. It really is a beautiful day. 
I won't get cloud cover for another couple hours.
It's 4:00, I think I'm done for the day. I never got the cloudy day. It was good for the flowers though, tomorrow should be the one where I can glaze in all my colors, I have all the shapes right.

This is whiting out corrections, it will take two coats for a clean start.
Day 5, to catch each pattern of the tree correctly, look at the tree and paint it with one eye. 
Just relax yourself, you can do it.

Using one eye to view the painting and the image, which are stacked over one another is key, the most important drawing factor.

The other :) is to paint with two eyes open after you have mentally found your marks with one eye only :)

It's been a great day, just the right amount of overcast. 
My strokes are getting smaller so I think I can see the light at the end of the tunnel.

There is as much character in a tree as on a face, and much more intricate.

3:00, I'm adding the little branches that make the larger branches look real. A #3 script liner now that I have the patterns in  place. I'm looking for the details that make the character of this type of tree. The petals are usually darker green underneath. that's because they are pods of flowers, each pod sticking out from the green leaves. that always casts a shadow in the sun and even in cloudy weather. the green leaves are very small on a shaft like a feather.
I'll try to mimic that in a stroke.

The tree is 30% covered now, way up from when I started. The petals are bluer purple in the shade and redder in the sunlight. The leaves go from a purple-green split complementary to a yellow-green opposition to the purple. It's Great the way nature works that way.

The colors remind me of the first transparent yellow Giotto's painted with. Arsenic, his green would have been an iron green. He couldn't use the copper sediment which would have been better and more transparent because lead turned copper black. If he had Egypt's tin white it would have been easier. We have come a long way since than as far as poison pigments and compatible colors are concerned but today we don't have a transparent yellow  acrylic. It's that old  Church-Ostwald Color Chart  where manufactures match their colors to. We really do need an overhaul on how we use color pigments.

Here is the day 5 image.