A few weeks ago I got a new easel especially for drawing while sitting down. It is a sturdy field easel and I sit in front of it on a flexible low stool. I tilt the drawing board at 45 degrees. But I get the impression that my drawings have been a fraction distorted lately. So now I wonder if I’m doing something not quite right. I have checked the tilt, which is correct. Perhaps the height of the worksurface?