This is about as clearly as I've found the procedure spelled out - https://wiki.bentleypublishers.com/display/tech/Mercedes-Benz+E-Class+Owner's+Bible+(1986-1995),+Update with the caveat that some models have the image of a ramp rather than tick marks on the tension scale.

If that's not enough, here's a discussion site for NY shops - New York - PeachParts Mercedes ShopForum

Sixto
87 300D