--- ray/src/rt/t_data.c	1989/03/14 11:31:17	1.1
+++ ray/src/rt/t_data.c	1989/04/11 13:30:37	1.3
@@ -57,10 +57,10 @@ RAY  *r;
 		objerror(m, USER, "bad # arguments");
 	sa = m->oargs.sarg;
 
+	for (i = 7; i < m->oargs.nsargs && sa[i][0] != '-'; i++)
+		;
+	nv = i-7;
 	if ((mxf = (XFORM *)m->os) == NULL) {
-		for (i = 7; i < m->oargs.nsargs && sa[i][0] != '-'; i++)
-			;
-		nv = i-7;
 		mxf = (XFORM *)malloc(sizeof(XFORM));
 		if (mxf == NULL)
 			goto memerr;
@@ -103,11 +103,10 @@ RAY  *r;
 	if (errno)
 		goto computerr;
 
+	multv3(disp, disp, mxf->fore.xfm);
+	multv3(disp, disp, r->rofx);
 	for (i = 0; i < 3; i++)
-		r->pert[i] += (	disp[0]*mxf->fore.xfm[0][i] +
-				disp[1]*mxf->fore.xfm[1][i] +
-				disp[2]*mxf->fore.xfm[2][i] )
-					/ mxf->fore.sca;
+		r->pert[i] += disp[i] / (mxf->fore.sca * r->rofs);
 	return;
 dimerr:
 	objerror(m, USER, "dimension error");