QDB2VAL
lval = QDB2VAL(ctl, sleft);
rval = QDB2VAL(ctl, sright);
*left -= VAL2QDB(ctl, lval) - VAL2QDB(ctl, QDB2VAL(ctl, zleft));
*right -= VAL2QDB(ctl, rval) - VAL2QDB(ctl, QDB2VAL(ctl, zright));