Refer to figure.
The Point of Safe Return (PSR) is the last point on a route at which it is possible to return to the departure airfield arriving back with the required fuel reserves still available in the tanks. If the pilot chooses to continue past the PSR, he is now committed to landing at your destination.

Time (to PSR) = E x H / 0 + H

• Where, E = Safe endurance based on available fuel; H = Ground speed home; 0 = Ground speed out

Solving from Heading (HDG) & Ground Speed (GS), knowing WV, TAS and required track.

1. Set wind direction to 260º under the "TRUE HEADING" index at the top.
2. Set the center point on the True Airspeed (TAS) of 140 kt.
3. Mark the wind velocity 30 kt down from the centre point.
4. Initially, set the True Track under the "TRUE HEADING" index.

• GS home: 165º

5. Note that this heading would result in 12ºL drift and a track of 153º.
6. Reduce the heading value under the index until the heading minus the drift gives a track of 165º. This occurs at a heading of 177º with 12ºL drift.
7. The groundspeed for this track is approximately 139 kt.

• GS out: 345º

5. Note that this heading would result in 12ºR drift and a track of 357º.
6. Reduce the heading value under the index until the heading plus the drift gives a track of 345º. This occurs at a heading of 333º with 12ºR drift.
7. The groundspeed for this track is approximately 134 kt.

We can now apply the formulas:
Time (to PSR) = E x H / 0 + H
Time to PSR = 4.5 x 139 / 134 + 139 = 2.29 h

To find the distance from the departure airport to the PSR, we simply multiply the time to PSR by the GS OUT: 2.29 h × 134 kt = 307 NM.