--- ray/src/rt/t_data.c	1989/03/28 07:44:15	1.2
+++ ray/src/rt/t_data.c	1989/04/19 21:20:28	1.4
@@ -48,6 +48,7 @@ RAY  *r;
 	int  nv;
 	FVECT  dval, disp;
 	double  pt[MAXDIM];
+	double  d;
 	DATARRAY  *dp;
 	register XFORM  *mxf;
 	register char  **sa;
@@ -103,11 +104,11 @@ RAY  *r;
 	if (errno)
 		goto computerr;
 
+	multv3(disp, disp, mxf->fore.xfm);
+	multv3(disp, disp, r->rofx);
+	d = 1.0 / (mxf->fore.sca * r->rofs);
 	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] * d;
 	return;
 dimerr:
 	objerror(m, USER, "dimension error");