I would like to describe a speedometer. Here are 3 ways I can phrase the sentence:

The dial shows the speed at which the car is moving.

The dial shows the speed which the car is moving at.

The dial shows the speed the car is moving at.

I'm pretty sure the first 2 are equivalent and I'm not sure the 3rd is grammatical, though I do hear it spoken. For the purpose of (current) technical writing, is any of the above preferred?

  • They all have the same meaning -- just three different ways of saying the same thing. The syntax is different of course and the first example is somewhat more formal than the others. – BillJ Dec 24 '17 at 11:08
  • @BillJ Maybe you would like to post an answer. Are you saying that the which in the 2nd sentence is redundant? – user1803551 Dec 24 '17 at 11:18
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    Yes, "which" is omissible because it is complement of the preposition "at". It is only when the relative word is subject of the relative clause that it is not omissible, e.g. "I bought some new batteries [which solved the problem]", where "which" is subject of the bracketed relative clause and is thus obligatory – BillJ Dec 24 '17 at 11:25
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    '... at which the car is moving' is also 'redundant'. 'This dial shows the speed of the car' is more streamlined, less Model T. – Edwin Ashworth Dec 24 '17 at 12:29
  • BillJ's "somewhat more formal" translates into the real world as: If you want to sound like a yokel from the rural South, use the second or third sentence in written work. – KarlG Dec 24 '17 at 12:44

The dial shows the speed of the car.

Logically, wouldn't this be precise enough for a technical writing?

Options 1 and 2 are correct, hands down. Option 3 is neither incorrect -- 'at which' is implied there.


Avoid "orphaning and marginalizing" the preposition -- I mean, don't separate it and move it to the end of the sentence, show some consideration for the reader.

That said, and the preposition in its place, you cannot dispense with which anymore.

The dial shows the speed at which the car is moving.

That makes life simpler, though the sentence a bit longer.

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    Whoever downvoted this, I would like to know why. – user1803551 Dec 24 '17 at 12:50

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