Study materials
This sentence is grammatically flawless and unreadable at first pass.
Although the results, which were obtained under conditions that differed from the approved protocol, appear consistent, further verification is required.
The results appear consistent. They were, however, obtained under conditions that differed from the approved protocol, and further verification is required.
Editing a complex sentence begins not with cutting but with asking where its subject is and where its verb is.
The distance between subject and verb
The most reliable measure of readability is not sentence length but how many words stand between the subject and its verb.
The results, which were obtained under conditions differing from the approved protocol, appear consistent.
The results appear consistent. They were obtained under conditions differing from the approved protocol.
The practical limit is one short insertion. Two in a row and the reader loses hold, and the sentence has to be read again.
Hierarchy: what is main and what is background
In a complex sentence one idea is the main one and the rest are subordinate. If every part carries equal weight, the reader does not know what to remember.
The method is fast and it requires special equipment and it is expensive.
Although it requires special equipment and is expensive, the method is fast.
Coordination levels; subordination builds hierarchy. In editing you are deciding, above all, what to make the main clause.
Where to put the complexity
English tolerates a long tail far more easily than a long insertion. So an editor's first move is to shift the heavy material to the end.
The question of whether the data had been verified independently arose.
The question arose of whether the data had been verified independently.
Where it breaks down
The first failure: the sentence was split and the link between the halves disappeared.
The results appear consistent. Further verification is required.
The second: simplification destroyed the hierarchy.
The method is fast. It requires special equipment. It is expensive.
The third: the editor invented a relation that was not there.
The costs rose. Therefore, we changed supplier.
All three are caught by one question. After the edit, are the relations still the ones the original had?
Try it right now
Take the longest sentence in your writing and split it in two so that subject and verb sit together in each.
Then check whether a logical link disappeared. If it did, restore it with one word.