Absent nouns

Here's a good example -

Das Zentrieren und Verriegeln erfolgt über Führungsbolzen und Verriegelungseinheit.

I have already whinged about the use of erfolgen, so I will ignore that. Here is my translation

"Tools are centred and locked by locating pins and a locking unit."

The interesting bit is where does "Tools" come from. Werkzeug does not appear in this sentence, nor in the one above it if the truth be told. It is in the context, which translators are supposed to keep in their head. This means you not only have to chunter through sentence by sentence, as encouraged by the use of translation software. You have to understand what the document is covering and fill in the absent nouns.

I suppose you could translate it as

"Centring and locking is done by locating pins and a locking unit"

but I feel uneasy with that. Exactly what is centered and locked?

For the engineer who wrote the documentation it was obvious, so he/she didn't bother to write it down. I often feel that something is missing. I have not yet made my mind up whether it is idle engineers or something fundamental about German. It seems to contradict repeated noun use, which is surely a tendency in the other direction...