What is the point of throw the rock?

In this scene they throw and measure the time to reach the ground. They measure 6 sec.

But what is the point if they are going to jump with the squirrel flying suits. At the end the scene last for 2 min 20 seconds.

I would understand if that was a regular base jump where you need to syncronize opening the parachute. But not when you will doing lot of your flying horizontally.

Best Answer

They are preparing to BASE jump off of a non-vertical cliff, with a transition into wing-suit flight. When BASE jumping, there is no initial forward movement (or more correctly, only what the person provides him/herself.) So, initially, they would be dropping vertically, until building enough flow through the wings to transition to forward glide/flight. By dropping the rocks, they can judge the vertical distance to the first solid object below, to determine if there is enough height to survive before the suits propel them forward enough to miss that impact.

A couple old adages apply here, in that it's not the fall that kills you, it's the sudden stop at the end, and flying is learning how to throw yourself at the ground and miss.