Where to get in NZ: www.mapsport.co.nz, http://www.grassyknoll.co.nz, www.compasspoint-online.co.uk
Typical Retail price: ~ $150
The Silva Race S Jet Spectra is the ultimate tool for orienteers and adventure racers. It is a simple compass for making quick and accurate bearings if you know what you are doing. Because these are premium tools for navigation they can be delicate and they can be expensive. Surprisingly for such a small tool they are packed with all sorts of features, almost everything you might need in the middle of a race to get you where you want to go fast! I have had 5 of these over the years and have been pretty happy with how they have lasted and how they have performed.
The main function of a thumb compass is to allow you to hold a map and a compass in the same hand at the same time. This allows you to take accurate bearings and keeps you in contact with the map the whole time. This is very important for orienteering, maybe less so for Adventure racing, but with the development of navigation in adventure racing the thumb compass is also making a good showing. In adventure racing of course some preparation of the maps to offset magnetic north is often required if you want to use one.
To use a thumb compass and take a bearing its really easy, almost easier than with a base plate, effectively you are just eliminating one of the steps, turning the housing, the most complex one! On the map you line up the centre line of the compass with the leg you wish to travel, then without twisting your wrist turn your whole body so that the needle points to North on the map, then follow the centre line of the compass.The Spectra System is a Silva innovation to allow even quicker bearings. The idea behind the system is that you take the bearing, look down at the colour bar, and memorize it. Say it is: 2 dot yellow, then that’s all I need to remember each time I look down at the map.
This compass comes in two versions, the Left and Right hand version. Convention usually dictates you use the left hand for holding the compass. It is also important to get the right compass for the right magnetic zone, as the needles are balanced differently depending on your angle in the world relative to magnetic north!
The latest version of the Jet Spectra is allows you to place you thumb directly onto the map, the previous version did not. This is supposed to allow for ease of “thumbing” the map. I am unsure if it really makes a difference as I tend to use the tip anyway. Maybe having your thumb directly on the map gives you a better grip.
The compass also comes with some measuring bars, I don’t tend to use these much in orienteering as I go on “feel” more than anything when it comes to distance… could be my downfall sometimes too. On the odd occasion I may use them, but often the bars are not quite right for the scale you are after. In adventure racing, the maps tend to have a grid on them making the bars somewhat redundant, but without grid, they can be very useful!
The compass is attached to your thumb via and elastic strap. Its a very basic strap, with just a short length of strap required to tighten to ft comfortably to your wrist. I have to admit that I am slightly different from most people who use these compasses and I hold it in my right hand. General convention is that you are taught with using your left hand, keeping your right hand free for more complex tasks like punching controls etc. As a result of this I use a specifically designed right hand compass, and to make sure that it fits comfortably the first thing I have had to do on all of them is to turn the strap around so that the doubled up stitching does not rub on my thumb so much that it annoys me! Downsides of carrying a compass on your thumb comes about in longer distance racing where you can get cramp from holding it and your map together for long durations. However the biggest drawback comes in the cold weather, the strap attached to your thumb reduces the circulation and your thumb can get very cold as a result.
The jet spectra is made of a tough clear plastic, however there is only so many falls it can handle onto rocky ground. They will often break and leak the liquid from the compass housing, usually slowly if its just cracked or rapidly if there is a fatal breach! I have own 5 of these compasses and have broken only one of them myself. Others however have had much worse luck than me and have managed to break several as a result of falls.
The major flaw with the design of the Jet Spectra 6 was the thumb strap buckle. I have had 4 buckles break as a result of damage to the plastic, the problem being that it is made of a semi crystalline and brittle plastic, which does not allow for any give under impact loading or rough handling. In the end I replaced my straps with similar straps which are actually for sport ident sticks. The latest version the Race S Jet Spectra this compass has made significant improvements to the thumb strap and made the buckle out of a more ductile plastic.
Temperature or altitude variation can create a bubble in these compasses. Bubbles are bad because they can push the needle around, and push you off your bearing. Often its a sign that there is a leak in the capsule at lower levels! Keep an eye out for them as sometimes they can disappear altogether when returning to normal conditions.
The latest incarnation of this compass comes with the brightly coloured spectra system around the perimeter of the housing. The majority of the compass itself is clear, so that for functional reasons you can see the map underneath. It would be fair to say that the overriding design philosophy is definitely function over appearance. However its general looks make it look like a complex tool for a pretty specific job!
Because this compass is very specific for the job at hand you will find that the cost is pretty high compared with a standard compass. The benefits of having this tool I think justify the cost. With this system you get a stable and accurate bearing which in the long run is bound to save you time. So if you are serious about navigating, whether it be adventure racing or orienteering this is the ultimate tool.