There are no equations to determine the best investments.
There are theoretical approximations but we cannot depend on them 100%.
For a host of reasons, they don't tell all, and they don't always work.
The point is to be able to measure and conceptually understand what's going on.
You are probably better off knowing what questions to ask and making big-picture look-out-the-window risk/reward decisions than getting bogged down trying to calculate the risk of the investment yourself.
You can look at the numbers, particularly comparative numbers, to get an idea whether an investment more or less accomplishes your objectives.
You can also look at a chart to get a quick view or vision of the volatility without knowing the precise numbers within.
At the end of the day, quantitative measures are important mostly for comparison.
Some of your best investment calls will occur by simply looking out the window.
What is important is to grasp the concept and then with a few measures to help assess risk/reward and especially to compare it.