What is a key precaution when setting up a potometer?

When setting up a potometer, ensuring that all fittings are tight to prevent leakage is crucial for obtaining accurate measurements. A potometer is used to measure the rate of transpiration in a plant, which is directly related to how much water is being taken up by the plant. If there are leaks in the system, the water loss would not be a direct result of transpiration but rather due to the improper sealing of the apparatus, which could lead to misleading results.

Tight fittings ensure that the water only moves through the plant's vascular system and the apparatus, allowing for a clear understanding of the water uptake and transpiration rate. This is vital for effective experimental results, as any leaks would introduce variability that can compromise the study’s findings.

Other choices involve aspects of setup that do not significantly impact the integrity of the experiment when compared to ensuring tight seals, thus the emphasis on maintaining a leak-free potometer setup stands out as the essential precaution.