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 Arrange charts so that both the charts and the controls of the helicopter may be easily managed at the same time. A chart should be folded so that the section being used is readily available, with a minimum of refolding or handling in the air. If more than one chart is to be used, they should be pre-arranged in the order in which they will be required. Align the chart so that the required track on the chart will be parallel to, and pointing in the same direction, as the track being flown.
The recommended practice in navigation by map reading is “from watch to chart to ground”, in other words, noting the time, studying the chart, and anticipating what is to be seen on the ground. There are times, however, such as when you are lost, when the reverse procedure is more valuable, i.e., relating features on the ground to features on the chart. A great deal of practice with both methods is required at varying altitudes and on different headings.
Estimating
To become proficient in pilot navigation, you must develop the ability to estimate. This can only be done through practice and more practice. While in flight, estimate the bearing and distance the helicopter is from a heliport, town or check-point, observe the natural signs of surface winds and estimate their direction and strength; estimate the size of objects on the ground and the distance they are from each other. When passing near a spot that you could consider for an emergency landing, estimate its suitability. Look quickly at a chart and estimate the distance that a certain lake is from the helicopter, what heading will be required to fly to it, and how long it will take to get there.
The more you know about the subject of navigation, the easier and more accurate estimating will be. 
Tracking Errors and Corrections
Owing to inaccuracies in the forecast wind and in flying the helicopter, errors often occur that require alterations of heading to bring the helicopter to the destination. Before corrections are discussed, the following terms must be defined:
1. Required Track. The proposed path of the helicopter over the ground.
2. Track Made Good. The actual path of the helicopter over the ground.
3. Track Error. The angle between the required track and the track made good, measured in degrees, and always expressed as being left or right of the required track.
4. Opening Angle. The angle between the required track and the track made good.
5. Closing Angle. The angle between the old required track and the new required track to arrive at the destination.
Ten Degree Drift Lines
In Figure 20-1, 10-degree drift lines are shown opening up from the set-heading point and closing down to the destination. These lines enable the pilot to estimate track errors and required heading changes with reasonable accuracy.
Point A in Figure 20-3 indicates a point on the track made good which is 7 degrees to the left of the required track, indicating an opening angle of 7 degrees. The angle can be estimated more accurately by imagining or physically making a mark at the mid-angle of 5 degrees (line B) and establishing the pinpoint in relation to that mark. Closing angles may be determined in the same manner, using the 10-degree drift lines, which converge on the destination. The angle between the required track and a line joining Point C to destination indicates a closing angle of 4 degrees.
 

 
Figure 20-3: Track errors and opening and closing angles
 

 
Figure 20-4: Double track error method 
Heading Corrections
Once you have established the position of the aircraft accurately, and provided it is not on the required track, decide upon the best course of action. Normally, approximately 10 to 25 miles should be flown before attempting to estimate any track error, because errors over a short distance are magnified considerably. The heading of the aircraft can be changed so as to either return to the required track, or else fly directly to the destination. This will depend on the position of the aircraft. It is usually more desirable to return to the required track since the route study has been concentrated on that area and, in addition, a line already drawn on a chart is much easier to follow.
　
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