Suunto Vytec

[NudeDiver]

You can cut paper with a knifeor a pair of scissors or an axe, but no one would ever class axes and scissors as "kinds of knives".

Sure they are. Much as a screw is simply an inclined plane wrapped around a cylinder.

 

[bleeb]

As I have ementioned many times before, there is no such thing as a "digital" compass. It is a digital readout for a miniature compass. It still uses a magnetic needle to align itslef to the earth's magnetic field as every compass eve built for the past 3 thousand years.

Actually, the majority of so-called digital compasses in consumer electronics including most cell phones and GPS receivers are all solid-state, usually Hall effect sensors, most often made out of silicon. No magnets or moving needles involved; chips with no moving parts, so generally cheaper and more reliable than any mechanism. Any magnetic interference comes from the stray magnetic fields that any lump of electronics and batteries moving electrons around will generate.

Do you know for a fact that Suunto isn't using Hall effect sensors?

 

[ClayJar]

As I have mentioned many times before, there is no such thing as a "digital" compass. It is a digital readout for a miniature compass. It still uses a magnetic needle to align itself to the earth's magnetic field as every compass eve built for the past 3 thousand years.

A digital compass is actually *quite* distinct from your classic magnetic compass. In your classic magnetic compass, you have a small movable magnet which aligns itself with the local magnetic field. A digital compass, on the other hand, takes advantage of the fact that charged particles moving through a magnetic field are deflected in a direction normal to both the direction of the magnetic field and the direction of motion of the charged particles. (Actually, this is the same phenomenon that classic cathode ray tube televisions made such amazing use of.)

In the case of a Hall-effect sensor, which is a semiconductor device (like a diode or transistor), the current flowing through the sensor (which is *minuscule*) from one end to the other in the presence of a magnetic field (such as *earth's*) yields an even more minuscule potential difference from one side to the other. This tiny potential difference is what is measured and processed to give a heading.

The digital compass in, for example, a Suunto Vyper2 is a "one-axis" electronic compass. It is sufficient to tell heading, but only when held very close to level. The first consumer GPS receivers we geocachers used were similar, and the results were just slightly better than pathetic. More recent GPS receivers use multiple Hall-effect sensors in order to be able to compute heading in three dimensions, which allows them to tell you your direction regardless of the angle at which you're holding the GPS receiver. (Their algorithms generally project the heading vector onto the plane of the local surface of the earth, although it would be quite cool to have a dive computer that gave you a true three-dimensional heading.)​

The two magnetized needles, one from the digital compaas and one from the "analogue" compass, will be attracted to each other rather than swing in the earth's magentic field.

You can see what happens when you put two normal compasses together. The same thing will likely happen with the Viper2 in the same console as the compass. The result: you're really going to get lost!

The magnetic field of the classical compass can be significant. It has to be strong enough to quickly move a needle -- more often, an entire compass card (as the disc with markings is called). Having two such compasses near each other can *certainly* pose a problem. On the other hand, there is no such issue with the *minuscule* magnetic field caused by the tiny currents in the computer. (If they had an electromagnet strong enough to affect an SK-7, the battery life would be on the order of *minutes*. :biggrin

It is *utterly* irrelevant to an SK-7 that there is a digital compass nearby. On the other hand, with the substantial magnetic field of an SK-7, placing it right next to a Vyper2 will almost certainly cause the Vyper2's digital compass to misread. (If you want me to make a video and post it on YouTube, I can certainly do that. I just tried it out, just to make sure there wasn't some confounding factor I may have missed, and the effect is indeed dramatic. Facing north, both compasses read north. When I bring them together, the SK-7 has not moved at all, but the Vyper2 has practically flipped almost to due south thanks to the magnetic field from the SK-7.)

With any luck, this generation of computers will be the last one we see with this useless, and potentially dangerous, device embedded.

Hopefully, I've done at least a little to help clear up your misunderstandings. Electronic compasses are certainly not useless (although I prefer the better visual feedback and usability of my SK-7). Calling them "potentially dangerous" is untenable (especially when we strap virtual bombs to our backs and tempt fate every dive ). Of course, if you have an SK-7 mounted adjacent to a computer with a digital compass, the digital compass is not usable, so I will concede that minor sub-point. (The regular old magnetic compass is completely unaffected, of course.)

Frankly, I don't much care for mine, but I have jarred my SK-7 on a dive before. It jumped the fulcrum and the card jammed. Had I needed it, the jam-proof electronic compass on my Vyper2 could have come in quite useful. (I consider it a worthwhile backup.)