Before shipment, the factory adds in some water droplets to the tester's cap to maintain a hydrated atmosphere for the probe. This ensures that the pH sensor keeps its sensitivity. Therefore, users can begin using their tester immediately upon receiving it. 

This practice of adding several drops of water into the cap for storing the tester is highly recommended for those who use the tester regularly. However, if the tester had not been used in a long time (eg > 1 month), or you feel like the tester's response time is much slower than before (takes a lot longer to reach a fully stable reading) , you can soak the probe in 3M KCL solution overnight to recover its sensitivity.