Difference between Wet Bulb Temperature in Weather file and Results

My Question is in CSP Trough Physical Regarding WBT Data(Wet Bulb Temperature).We can take this data from two ways first from Location & Resource weather Data Viewer & second is from Output window view & Export Data -Time-series. But for same weather file the data taken from both the ways(as mentioned above)is different. My question as follows, 1. Why it shows difference? 2. Which data we should take?
SAM calculates the wet bulb temperature from the atmospheric pressure, dry bulb, and relative humidity values in the weather file. This calculated value may differ from the wet bulb temperature in the weather file. The value in the SAM results is the value that SAM uses in calculations.
SAM uses the wet bulb temperature in the power cycle cooling equations.
Best regards,

Paul.