I am told that there devices that clip on to the hard line to sense the stress developed by the pressure build-up during the injection pulse. It controls a timing light. With this you can time the engine much like a gasoline engine.
This subject comes up several times a year.
In order to use the timing device as you describe you have to have already timed your Engine according to the Mercedes spec. (That is a Static timing.)
Then you hook up the above described Tool and see what degrees the Timing light tells you when the Engine is running and you have created your own spec for your Engine. You also need to note the rpm that timing was done at.
(This is Dynamic Timing and Mercedes has no specs for Dynamic Timing.)
(Also remember the Timer on the Mercedes Engine advances the Begin of Injection.)
So you cannot just go out and buy the Tool; clamp it on and use it to time your Engine.
The above described Tool favors a person who has several of or a Fleet of the same vehicles.
Some Mercedes Fuel Injection Pumps; I believe after 1982 can use something called an A&B Light because that have a port on the side of the Governor Housing that allows the A&B Light and also a Timing/Locking Pin to be used.
The A&B Light and Timing/Locking Pin reference on a raised spot on the Fuel Injection Pump Camshaft/Governor. (Again a Static Timing.)
To ID if your Fuel Injection Pump can use the A&B light or the Timing Pin look for the Oval Plate with the 2 screws pointed to by the Blue Arrows and a large Central Plug in the Red Circle.