It's true, they don't need to be exact. Truth is, I just point mine toward the nearest metro area and usually do okay. But last time, I actually had to dig out the phone and look up the towers. I had 2 towers in range, and they were opposite directions... Also, fine tuning by turning the antenna works for me too. I use the compass on my phone to get a bearing.
The arrow on your rotator inside the TT does not indicate the direction of the antenna, it indicates the direction for storage. The signal direction is indicated with two TINY hashes on the ring. You can feel them more than see them, and once I found mine, I marked them with a Sharpie.
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!