We are all familiar with the requirement to report our ops status and position to whomever is maintaining our radio guard, normally at 30-minute intervals. Of course the reason for this is to keep track of you for your safety, and to take action to find you in case something happens and you do not check in. Also, by knowing your position your OPCON can more efficiently assign assets in the particular AOR as needed.
I sometimes hear crews read off the numbers on their GPS to the third decimal place while reporting their position which is way too precise. For example, the latitude on the unit might read
This should be reported as “Three Seven Degrees, Four Niner Decimal Three North”.
Why not report it all? Well, for a couple of reasons – the first is brevity, to keep the transmission as short and meaningful as possible. Additionally, a more detailed position does not add any value for this purpose.
Let’s review what these digits represent. Recall that one minute of latitude (the “9” digit above) is equal to one nautical mile (2000 yards). One tenth of a minute (the “3” digit above) represents one tenth of a mile. That’s only 200 yards – plenty accurate to find you if necessary. If you’ve taken the AUXSC&E course (which is great…) you learned that the sweep width and derived track spacing for a facility-sized target is roughly 1-6 NM depending on several factors so one-tenth of a mile reporting precision is plenty good.
The hundredth digit (the “0” above) is equal to plus or minus 20 yards – that’s only two or three boat lengths. And the thousandth digit (the “2” above) is only plus or minus six feet! No one cares on which side of your boat you installed your GPS antenna.
Now, if you were reporting something that would benefit from the greater precision (such as during an MOB event) then additional accuracy would be appropriate to identify the last known position and the resulting CSP.