Yes - to set an equipment's pricing to per sample rather than per hour/day, first press edit on the selected equipment and go to the pricing tab. Leave the Internal price (hourly price) as 0, and create an instrument Add-on. Select User specified under Quantity, and then you will be able to select Per sample under Unit.
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Set the price per sample, and then save the changes. Now when your user creates a booking, they can choose the add-on and input how many samples they require, and the price will be applied.

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