Suppression of the leading zero in the time display.

Src/clock.c

@@ -230,7 +230,11 @@ void showTime(void) {
   }
 
   tube4_t buf;
-  buf.s8.tA = Clock.Hr >> 4;
+  if ((Clock.Hr & 0xf0) == 0) {
+    buf.s8.tA = TUBE_BLANK;
+  } else {
+    buf.s8.tA = Clock.Hr >> 4;
+  }
   buf.s8.tB = Clock.Hr & 0xf;
   buf.s8.tD = Clock.Min >> 4;
   buf.s8.tE = Clock.Min & 0xf;