Turbulent air? Why on earth are you trying to use the chart in the air?? That's the dumbest thing I've ever heard.
Go up and have someone sit in the left seat with a paper and pen. (Believe me, you won't have to look hard for someone who wants to go for a helicopter ride.) Set your power, then *you* read the numbers to them and have them write those numbers down. Then land. Now, in the safety and non-turbulent comfort of your desk, open the RFM and plot the numbers.
Sheesh, make it easy on yourself, man!