undef("centerat") procedure centerat(plot[1]:graphic,x[1]:numeric,y[1]:numeric) local vpx,vpy,vpw,vph,cx,cy,dx,dy begin getvalues plot "vpXF" : vpx "vpYF" : vpy "vpWidthF" : vpw "vpHeightF" : vph end getvalues cx = vpx + vpw/2.0 cy = vpy - vph/2.0 dx = x - cx dy = y - cy setvalues plot "vpXF" : vpx + dx "vpYF" : vpy + dy end setvalues end