diff --git a/m10/m10x.c b/m10/m10x.c
index 6f152ad..8e8b95e 100644
--- a/m10/m10x.c
+++ b/m10/m10x.c
@@ -553,7 +553,8 @@ int get_SN() {
     sprintf(datum.SN, "%1X%02u", (byte>>4)&0xF, byte&0xF);
     byte = sn_bytes[3] | (sn_bytes[4]<<8);
     //sprintf(datum.SN+3, " %1X _%04u", (byte>>12)&0xF, byte&0xFFF);
-    sprintf(datum.SN+3, " _ %1u%04u", (byte>>13)&0x7, byte&0x1FFF);
+    //sprintf(datum.SN+3, " _ %1u%04u", (byte>>13)&0x7, byte&0x1FFF);
+    sprintf(datum.SN+3, " %1X 1%04u", ((byte>>13)&0x7)<<1, byte&0x1FFF);
 
     return 0;
 }