The direct translation is this:
"The sample is to be measured with 4 widgets in turn (***4) so that the approximate distribution of the apparatus is taken into account in the assay."
"sample": means sample, which is not disputed
"alternately measured": means measured in turn, sequentially in order
"unit": means many things, generalized to mean unit, unit, individual, and since it's on the apparatus, it should mean parts
" approximate":means approximate, there is no dispute
"device" and "distribution" of the two words have a problem, the meaning of device is "equipment, apparatus", and distribution means "distribution", and the meaning of the word "distribution". "test, examination".
Medical English is not easy to translate, this is just as a reference, I hope it will help you
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