Wetbulb and drybulb readings

[Slade Smith]

Thank you in advance.. I have a psychrometer and it says that i can test the wb and db of the return and supply..How am I to measure? should I drill a hole at the end of the return and at the beginning of the supply to get the reading?

[Mr Bill]

Thank you in advance.. I have a psychrometer and it says that i can test the wb and db of the return and supply..How am I to measure? should I drill a hole at the end of the return and at the beginning of the supply to get the reading?

Is this a vertical or Horz. application?