18.58.2 Define and calculate:
(a) time and distance to the point of no return (PNR);
(b) time and distance to a departure/destination equi-time point (ETP).

point of no return (PNR)

departure/destination equi-time point (ETP)

Equi-time Point is important to know when you have a problem you need to know quickly  what to do, are you go return to your departure point or carry on to your destination.

Notes:

Given that you need to workout a general half way point with these calculations, however ground speed out and back could be different thus move the actual position you are looking for.

So that we need here is to set up a ratio using the Ground Speeds.
( frac{1}{1+1} )  or ( frac{1}{2} ) Which Halfway or .5 
( frac{GS Home}{GS out +GS Home} )  GS Out and GS Home are the same the then equal to Halfway or .5 

Working with a Head Wind our ground home is more than our ground speed out

( frac{GS Home=2}{GS out=1+GS Home=2} ) = ( frac{2}{1 +2} ) = ( frac{2}{3} ) now our ETP is passed Halfway or .66

Working with a Tail Wind our ground home is less than our ground speed out

( frac{GS Home=1}{GS out=2+GS Home=1} ) = ( frac{1}{2 +1} ) = ( frac{1}{3} ) now our ETP is before Halfway or .33

18.70.2 Explain the limitations of using GPS/GNSS to supplement normal visual navigation.
Sub Topic Syllabus Item

18.50.2 Describe the techniques, requirements, and procedures for:
(a) re-establishing position if lost or unsure of position;
(b) diverting from the pre-planned route;
(c) navigating at low level when forced to do so by bad weather;
(d) amending SARTIMES.

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18.48.2 Describe the techniques and procedures for:
(a) setting heading;
(b) cruise routine/activity cycle;
(c) maintaining a flight log;
(d) turning points;
(e) approaching/rejoining at a destination aerodrome.

18.46.2 Derive, from a sample Aircraft Flight Manual, the fuel consumption rate for a given
leg.

18.44.2 Complete a navigation log / flight plan for a VFR cross-country, including calculating
the following values:
(a) top of climb point;
(b) level cruise portion;
(c) top of descent point;
(d) CAS/TAS;
(e) tracks;
(f) estimated wind velocities;
(g) estimated temperatures;
(h) headings;
(i) groundspeeds;
(j) distances;
(k) EET;
(l) ETA;
(m) SARTIME.

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18.42.2 Mark the following on a map:
(a) departure aerodrome, turning points, and destination aerodrome;
(b) tracks;
(c) heading change markings, either 1:60 or drift lines;
(d) ETA amendment markings.

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18.40.2 List the factors to be considered when selecting a VFR cross-country navigation route.

18.36.2 1 in 60 rule computations.
Flight Planning

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18.34.2 Identify and label the three vectors of the triangle of velocities.