Quoted from Rick471:6.3 degrees is what I have heard is the most common setting. Thats what I have mine on...
I use this for best accuracy. Works Great!
http://www.sears.com/craftsman-digital-torpedo-level/p-00948295000P?currentProductTitle=craftsman%2ddigital%2dtorpedo%2dlevel&partNumber=00948295000P&storeId=10153&isSEOCanonURL=true&PRODUCT_TITLE_BRAND=craftsman%2ddigital%2dtorpedo%2dlevel&catalogId=12605&catgroupId=00948295000P&pageInd=product&i_cntr=1325886464727
yep that works awesome