changed M220

Firmware/Marlin_main.cpp

@@ -4936,11 +4936,15 @@ Sigma_Exit:
       SERIAL_ECHOLN("");
     }break;
     #endif
+
     case 220: // M220 S<factor in percent>- set speed factor override percentage
     {
-      if(code_seen('S'))
-      {
+	  if (code_seen('B')) //backup current speed factor
+	  {
 		saved_feedmultiply_mm = feedmultiply;
+	  }
+      if(code_seen('S'))
+      {		
         feedmultiply = code_value() ;
       }
 	  if (code_seen('R')) { //restore previous feedmultiply