Rules.md

@@ -18,3 +18,10 @@ We have a set of reserved variables that should be used throughout the project:
 | user | User database entry | some like new_user, s_user |
 
 Remember: Special cases aren't special enough to break the rules.
+
+Beside this, more relaxed, the use of following things is suggested:
+
+| Variable| What for| 
+| ------ | ------ |
+| m_type | Measurement type database entry |
+