The survey above the roof

On the roof, the wind pushed the paper record against my hand whenever I lifted the clipboard. The sensor's serial number was on its underside, so I had to read it using a small mirror. Salt had obscured the last two digits. Below us, the ventilation fans made it difficult to hear my colleague's instructions. We could only remain in the marked walkway; the unit stood just beyond easy reach. Then a shower began, leaving bright drops on the lens of the mirror. We decided to pause rather than turn an incomplete reading into a confident entry.

Describe the difficulties of recording the sensor details. You may support your points with brief quotations.