Chem lab help: How would a wet flask contribute to the pressure of a reaction of CaCO3 and HCl?

Let’s say the % concentrations of CaCO3 (table 4) you obtain from trial #1 and #2 are consistent, while the concentration obtained from trial #3 is significantly higher. Demonstrate, how and where, a wet flask could be involved to explain such a result. Explain in great details. <- is the exact question. What I'm doing in the experiment is measuring the change in pressure when I mix an antacid tablet with HCl, and attempting to figure out the concentration of CaCO3 in the tablet with that data.. stumped on this question, though. Help?