Looking at buying Wixey WR550 to mount on my Delta 15" planer. Before I buy, want to understand how it works. If I want to take some boards down to a certain thickness, how would I go about doing this? Per their web site, I understand it measures the board thickness coming out of the planer but, how do you know the thickness going into the planer so you know how much to take off or how many passes to make? Randy