The way to do it is go to butchers with a small precision square in the pocket. And politely check their machine before cutting. Once they see the precision square, they will understand you mean it square... I have been laughed at but at the end i achieved mine, in terms of precision...

Better to know you as the Precision Loco. In Spain we say : El que no llora no mama, meaning if you don't cry there is no a tit for you