Running fix plotting

This is how we plot a Running Fix Position:
Assuming the course is 080° degrees and the speed is 8 knots, or 8 nautical miles per hour, we take a bearing of 045° degrees on Alfa rock at 0900, now convert the compass bearings to true bearings and we plot it on the chart.
After 30 minutes we take a new bearing on the same rock that reads 015°degrees, now convert the compass bearings to true bearings and plot it on the chart along with the new time – 0930.
Knowing the speed, the next step is to determine the distance that the vessel sailed from 0900 to 0930.
For that we use the formula: D is equal to S times T divided by 60, where D is the distance in nautical miles, S is the boat speed, and T is the time in minutes.
In our case: 8 knots times 30 minutes divided by 60 equals 4 nautical miles.
Using the dividers, we span a distance of 4 miles on the latitude scale which is closest to the course line, and which runs along the sides of the chart.
We applied this span on our course, placing one leg of the dividers on the 0900 LOP intercepting the course and the other leg on the course line.
Using the parallel ruler we transfer the 0900 LOP to the blue mark.
As we notice, the two LOPs intercept at the point RF.
This is our Running Fix position.