GPS (Global Positioning System) is basically a satellite navigation system from a network of satellites which orbit the earth and transmit signals to GPS handheld devices on earth. From comparing the time the signal was transmitted by a satellight with the time it was received, the GPS handheld device calculates the user's exact location. The time difference tells the GPS device how far away the satellight is, and with the distance measurements from other orbiting satellights, the GPS handheld device can then determine the user's exact location.

BENEFITS OF GPS TO THE DETECTORIST.
The Portable Antiquity Scheme (PAS) advises us all to make a note of our exact findspot location, by map or GPS. The PAS has informed us that all finds are evidence of human occupation, and can help us understand more about a geographic area or object type. In this respect as more finds are recorded, we will become able to trace patterns in the way that finds are distributed and these patterns will provide valuable distribution data for professional archaeologists. For members of The Pembrokeshire Prospectors Society, GPS is of great benefit for when we report our finds to Mr Mark Lodwick (Finds Co-Ordinator, National Museum & Gallery of Wales, Cardiff), who is our club Finds Liaison Officer (FLO). Using GPS will give a quick and accurate findspot reference for us to record our finds. Another benefit of using GPS is that one could, in theory, record the exact findspot of (eg) a hammered coin. Then maybe in a few years time, when perhaps detector technology has improved, you may own a more powerful detector. GPS would allow you to return and re-locate the hammered coin findspot and search over the ground again using your deeper seeking detector for coins you may have missed previously! GPS could also be very useful for beach detecting. When searching beaches you could record the findspots of any gold and silver rings that you find for future reference. (eg) a gold ring findspot may produce more gold rings the following year due to the way the tides and currents sift and deposit items which are of similiar size and weight.

HOW CAN GPS BE USED TO PLOT AND RECORD MY FINDS?
A handheld GPS receiver can plot the National Grid Reference (NGR) of a findspot in seconds: However this can vary, as some GPS handheld receivers are of different design.

To record a findspot using a handheld GPS:-

1. Stand over your findspot.
2. Then record the NGR using the GPS receiver.
3. Mark a plastic finds bag with the NGR using a permanent black marker pen (e.g) good pens to use are Artline pens.
4. Place your find in the finds bag.

Before recording the findspots of your detecting finds, make sure your GPS device is set to the correct United Kingdom Time Zone and Map Datum for the British National Grid. Most GPS receivers are made in America and are set to record longitude and latitude.

HOW ACCURATE IS A TYPICAL HANDHELD GPS?
Most GPS units display a 10 figure NGR (1 sq metre), however their pinpointing accuracy can be less than this, often between 10 and 15 sq metres. Detectorists using lower cost GPS receivers, like the Garmin etrex should be confident of getting the accuracy of an 8 figure NGR. Using a GPS receiver while out metal detecting will allow one's finds to be recorded with great precision. Any GPS with WAAS (Wide Area Augmentation System) capability, may allow findspot accuracy to less than three metres on average.

HOW MUCH DOES A HANDHELD GPS COST AND WHO SELLS THEM?
Low price GPS units can cost between £60 and £100. The more expensive GPS receivers can often get you more features, but this will not always get you greater plotting accuracy. Most retailers which supply camping and outdoor pursuit equipment such as Millets and Halfords, will usually supply them. However, the best deals can be purchased on the internet from companies such as www.Amazon.com or www.Globalgizmos.co.uk. Also why not try out the website www.Kelkoo.co.uk which compares various retailers prices, and get yourself a GPS bargain.

 

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