Use a calculator easy option I do
Recipricol bearings +2 -2 rule or -2 +2
220 -2= 020 + 2 = 040 and go the other way 040 +2 =240 - 2 = 220
only time you have to think is 190 as = 370 =010
I always use a calculator for STD I always check on the Plotter as well when drawing bearings and getting the recipricol (Portland type).
Secondary ports www.easytide.ukho.gov.uk
the more tools in your box the better equiped we are. Secondary Ports can be achieved by using Sharks tooth method or admiralty method practice using easy tide to check your answers.Same as plotting LAT AND LONG practice finding tidal diamonds on your chart then plot waypoints and find them. Practice is the key and so long as you have a method of checking your answers confidence will grow until it becomes second nature.Have fun