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The engineering team made a significant improvement to accuracy.


The engineering team made a significant improvement in accuracy.


I heard we can't use "in" here. Is this the case? What grammar rule says we can't use "in"?

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I wouldn't say 'in' is wrong.

It depends a bit on the context in which you want to say this. eg the accuracy of what?

Clive

Comments  
Students: We have free audio pronunciation exercises.

It's a gun.

in sounds fine.