I have used one of these many times in my lifetime. They used to be against the clocking in machine in factories and shops.  
This one is possibly mid century. Over time and possibly from use, the numbers have ghosted, however they can still be seen. 
These are great hung in the kitchen or hallway for the post that needs dealing with or with photos and cards displayed in them. An unusual place to store papers in a teenagers room and quirky too.
 
It is easily wall hung.
Measurements: 24 x 77.5cm high