My vacuum easel is "crowned" when not in use, but is as flat as I can measure when in use and a sheet of paper is in place. A very small rubber machinist's mallet, a dial indicator and a surface plate may be what you need to deal with your easels. After reading this: http://www.horolezec.cz/blog-engl/in...=item&itemid=5, I realize that I am a rank amateur when it comes to flatness......

Tim