The testo 606-2 actually shows three (3) different types of temperatures:
1) Air Temperature which is Dry Bulb (DB), this is always displayed on the lower right of the screen
2) DewPoint (td) or the surface temperature at which the current humidity will condense.
This is a setting you can call up, the DewPoint temperature will appear in the lower left side of display, and be followed by "td" to the right of the number
3) WetBulb (WB) a psychrometric calculation often used in HVAC system set up.
This is a setting you can call up, the WetBulb temperature will appear in the lower left side of display, and be followed by "WB" to the right of the number.
All three temperatures are likely to be very different at the same given conditions, as they represent different parameters.
Please check to see that your are reading the correct parameter, in same unit of measure (%, F or C) when you do a comparison to other meters.
If you would like help in setting the reading in the lower left of the display (to % humidity, td or WB) do not hesitate to call! 888-224-3437