How would you use the mental clock code to solve this dead reckoning problem?

Question

Can someone explain the question below in details?

You plan to fly a cross country flight at 2 000 feet at a true airspeed of 120 knots. Your track is 270° (True) and the wind is from 225° (True) at 24 knots. Using the Mental Dead Reckoning Clock Code, what true heading would you steer, and what would be your magnetic heading if the local magnetic variation is 4° West?

Answer 1

Step 1: Calculate maximum drift.

Max drift $ = \frac{wind speed}{TAS (NM/min)} = \frac{24}{120/60} = \frac{24}{2} = 12$

That means if you have a direct crosswind, you'll need to correct 12$^{\circ}$.

Step 2: Determine how much of the wind is crosswind

The mental clock code is a way of estimating crosswind component from total wind. There are 60 minutes on a clock face. If the wind direction is 60$^{\circ}$ or more, it's considered all crosswind, just as 60 minutes is considered the whole clock face.

By extension, a wind angle of 30$^{\circ}$ means 30 minutes, which is half a clock, so half the wind would be considered crosswind. 15 degrees would be a quarter of a clock, therefore a quarter of the wind, and so on.

Your maximum drift is 12 degrees with a full crosswind, but you don't have a full crosswind. Instead you have a 45$^{\circ}$ angle, so 45 minutes of a clock, which is $\frac{3}{4}$.

$ 12 * \frac{3}{4} = 9$ so you'll need to apply 9 degrees of crosswind correction toward the wind. $270 - 9 = 261^{\circ}$

Step 3: Correct for variation

"East is least, West is best". If variation is west, add to true to get magnetic.

$261 + 4 = 265^{\circ}$