At my age, I should have collected enough know how by now to know better and that I should never assume anything. In crafting, woodworking, sewing, knife sharpening or just about any task that require some precision never assume that everything is as it is. For example you might have used a 2x4 like a ruler or a level only to find out later after much error and frustration that the straight is not so straight. There is a reason we try to adhere to the motto "measure twice, cut once". In my case, it's, "measure twice, cut once, curse and repeat!" If you have a table make sure it's flat. How? By using a "standard" . Another material or tool that you know to be precise. If your ruler is warped. Try another ruler until you get the results you are looking for. I learned that lesson again for the first time. While using something that I "assumed" was flat and straight I ended up with poor results with my project and could not figure out why at first since I applied all the usual skills in the right order as last time. So I went back to the beginning and started again. Make sure the stone is flat. If not, make it flat. Then start your task or project again. After that my efforts were not in vain---SUCCESS. Relief.... and a sip of Limoncello to celebrate!