A right-handed person must write STAM with his right hand (a left-handed person must use his left hand). Writing with the non-dominant hand invalidates the STAM. STAM written by someone holding the quill with their foot or in their mouth is also invalid according to many Poskim. An ambidextrous person should use his right hand, but if he used his left hand it is kosher. If someone writes with one hand but does all other activities (like throwing a ball or eating) with his other hand, the Mishna Berura says he should not be hired as a Sofer.
-= 8 =-
-
STAM 101 introduction & index