diff --git a/uk_os/OSGM15_GB.sh b/uk_os/OSGM15_GB.sh
index 8d345f6..5d53db7 100755
--- a/uk_os/OSGM15_GB.sh
+++ b/uk_os/OSGM15_GB.sh
@@ -31,15 +31,16 @@ ETRS89_BRITISH_NAT_GRID='PROJCS["ETRS89 / British National Grid",
     AXIS["Northing",NORTH]]
 '
 RES_LAT=0.008983192446931791	# RES_NORTHING/(PI*GRS80_RAD/180)
-RES_LONG=0.00509465706621704	# RES_LAT*cos(MID_AREA_LAT)
-# RMSE = 0.000762624030848561m
+RES_LONG=0.015839681746927323	# RES_LAT/cos(MID_AREA_LAT)
+# RMSE = 0.0007570669375634179m
+# MAX_ERROR = 0.0019630308326981094m
 
 NO_DATA_VALUE="-32768"
 
 tail -n +2 ${SOURCE_FILE} | awk 'BEGIN {FS=","; OFS=" "} {print $2, $3, $6}' > osgm15_temp
 
 
-gdalwarp -r bilinear -dstnodata ${NO_DATA_VALUE} -tr ${RES_LONG} ${RES_LAT} -s_srs "${ETRS89_BRITISH_NAT_GRID}" -t_srs EPSG:4258 osgm15_temp osgm15_temp.tif
+gdalwarp -r bilinear -dstnodata ${NO_DATA_VALUE} -tr ${RES_LONG} ${RES_LAT} -s_srs "${ETRS89_BRITISH_NAT_GRID}" -t_srs EPSG:4937 osgm15_temp osgm15_temp.tif
 gdal_translate -mo "AREA_OR_POINT=Point" osgm15_temp.tif ${TARGET_FILE}
 
 rm ./osgm15_temp ./osgm15_temp.tif