Should It be 0.1 seconds instead?

What is the logic for having a marine chronometers ?

Thanks, PoliteMight.

They achieve a precision of around a 0.1 second loss per day.

Should it be 0.1 seconds loss instead? If so, why?

You haven't answered the above question.

Either one is acceptable. "Around a 0.1 second loss per day" is more conversational but both are understandable.

It is correct as written. Errors build up over time. Saying just "0.1 seconds loss" is unclear. Does that error occur every hour, every day, every year? "0.1 second loss per day" has the correct units. If you look up the error of a cesium clock, you find "1 second in up to 100 million years", again, error per unit time. If you just said "one second", that would be wildly misleading.

I may have misinterpreted the OP's question. I thought she was asking about "loss per day" in both cases but specifically whether the "a" was needed and shortened the phrase in her question.

They achieve a precision of around a 0.1 second loss per day.

or

They achieve a precision of around 0.1 second loss per day.

engineer is correct if "loss per day" is not included in the sentence.