When scanning in one position for longer time period a slight movement can occur in the scanner position due to changes in temperature.

Am I missing a comma in this sentence?

  • A comma is not necessary. But as @queeg pointed out, an a before longer would be expected; either that or make period plural. Also, watch out for those people who insist due to is "substandard" here and should be replaced by because of.
    – user6951
    Oct 3, 2014 at 13:32

1 Answer 1


Yes, you are missing a comma after period.

When is a conjunction in the sentence. If the when-clause comes before the main clause, we use a comma.

"When scanning in a position for a longer time period, a slight movement......".

  • 2
    You also, most probably, need to place an additional 'a' after 'for' but before 'longer'. 'one position for a longer time period, a slight' etc.
    – queeg
    Oct 3, 2014 at 9:13
  • A comma is not necessary, but some might find one useful.
    – user6951
    Oct 3, 2014 at 13:34

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