There is a widely-used rule of thumb in aviation called The 1 in 60 Rule. This rule is a method for approximating how far off-track you are, and what action is needed to correct your course so that you arrive at your intended destination.
Note: The word “miles” anywhere in this post refers to nautical miles.
In a nutshell, the rule states the following: For 60 miles of travel, a change of 1° in heading will result in being 1 mile off-track. So if you find yourself 3 miles off-track to the left after 60 miles, that means that your flight path was 3° to the left. You have a track error of 3°.
But you cannot simply turn 3° to the right, because then you will be flying parallel to your intended path. You must figure out the additional course correction needed to get yourself aimed back at your destination. If we realized our error halfway through the trip (with 60 more miles to go), the math is simple: Turn an additional 3° to the right, for a total of 6° heading change.
In life, as in aviation, It’s not always enough to know how far off the mark your efforts have been, you often need to be able to figure out how to get yourself back on-track. You need both measurements in order to hit your target.
The way we take measurements is to break our goals up into a series of milestones that lead to our final target. If you start missing your early milestones, it will alert you to the fact that you are no longer on track to hit your ultimate target. You’ll be able to see the gap between where you are right now, and where you want to be by the next milestone.