Compass Calibration Log: Fill & Download for Free

When I landed there years ago, I asked the almost-cliché old timer in ops (fine, he was a senior enlisted dude that was about 10 years older than me) about it. The most accepted tale seems to be that during the early days of testing, the pilots and engineers agreed that it was important to be able to calibrate the magnetic compass while airborne. Pilots would check right after take off and again before landing. They felt that being distant from the buildings was important to get a good read on the magnetic compass. This would let them know what the aircraft and its parts were doing to the compass. This would be logged on a deviation table and used in case the primary directional aides failed and pilots needed to use the wet compass. This is still a thing, but is more precisely measured these days.It sounded reasonable and we got our gas and left.

Watch sandglasses were used on ships to measure watch times, typically in half-hour periods. The helmsman or ship's page were the crewmen responsible for turning the watch sandglass, thus supplying the time to be registered on the ship's log; watch measurement began with the sun reaching its highest point—its zenith—at midday, which was likewise the essential time reference point for navigation. At that point in time, the ship's bell was struck eight times; after the first glass had emptied (half an hour), the ship's bell was struck once, after another glass, twice, and so on until four hours after midday, when it was again struck eight times. At that point, a new watch began, and the sequence was repeatedThey weren’t all that accurate, they could be resynchronized every midday when sun observation was possible; if coloudy then they’s have to stretch it a day.They also used a glass for recording speed… an important navigational detail so they knew how far they’ run (the compass telling them the heading) so thy could make the approximate position on a map. They used a log which was a rope with wood chips at calibrated intervals on it that was paid out during a fixed glass interval; the chips that paid out were counted during the time and it would give speed in knots directly.Ultimately ships chronometers took over, mechanical timepieces of great accuracy for the day, that some gained or lost on the order of a tenth of a second per day. By 1825, 20 years after M&C, they Royal Navy routinely installed them on all their ships.

The question is a false choice. A compass and a GPS device are both navigation aids. The compass will only indicate what direction magnetic north is. To use that data in determining your position you would need to supplement that data with other nav aids and have a proper chart or map (or local knowledge) in order to determine not only your position but the direction of travel required.The same is true with a GPS unit. A basic unit will give you latitude, longitude and the height in relation to the geoid. Like the compass that data in of itself is really pretty useless without additional data. Most GPS systems do include software that incorporates maps and charts and can also take the positional data and calculate the direction and speed of travel. I have used GPS units that only outputted the positional data and would have to plot that data on a chart to determine the direction and speed I was traveling. This is usually done every hour, between the known fixes I would use dead reckoning methods to keep the “best guess” (naviguessing ?) position and course.What GPS technology changed was the method one used to determine a reliable position. Prior to GPS one needed to use shore based radio navigation aids (Loran-C, ARGO, Mini-Ranger etc) to get a reliable fix. These radio networks were not only expensive to maintain but were rift with issues. Accuracy, range, calibrations and atmospheric effects were just some of those issues. You also could use celestial navigation, or as I call it “organic GPS”. You would also use good old fashioned dead reckoning and triangulation.What GPS brought to the table was a low cost and highly accurate positioning system. It also gave us a standard global reference, WGS-84.The following picture is of a ARGO radio nav station being setup in a remote area of Alaska. The tanks are for the propane generator needed to power the station.This is the antenna. The smaller one in the background is for the Mini-Ranger system used to calibrate the ARGO system. The antenna position is determined by using range and bearing from the nearest USGS survey marker. The position is than verified by running data from the WGS-72 transit sat system over about 7 days.Here is a typical Navigation system used for oceanographic surveying prior to GPS. The blue unit (bottom right) is the Mini-Ranger receiver. The two stacked units with the gray case and black faceplates (top right) is the ARGO receivers. The light blue unit (top left) is a rubidium clock used to increased the accuracy of the Loran-C unit to the right of it. The large unit on the left is the INS (Integrated Navigation System). It compiles and records the data from the numerous nav aids and sends basic data to a monochrome display (under the Loran-C).Now compare the above picture with the following one. This is the nav station on my last sailboat. The Raymarine unit is the INS system. It takes in raw data from two separate GPS units, radar, echosounder, fish finder, speed log, electronic compass, weather station, VHF and engine diagnostic data and numerous other systems that have a NMEA digital output. All in a small unit that costs very little to purchase (about $1200 including the radar and one GPS unit) and to maintain. All more accuracy. and reliability. That is what technology brought us.