Combining instrument uncertainty with repeated measurement uncertainty

I am using a digital manometer with a published accuracy of +/- 1%.

I took multiple measurements and, using Student's t-test calculated a 95% confidence interval based on the standard deviation of the measurements.

Do I need to combine the instrument uncertainty with the confidence interval based on repeated measurements? If so, how would I do so?

One source I found just used the larger of the two values. Would that be acceptable.