Iris 50 Compass Design oversight?

[microvise]

Anybody who has purchased a Plastimo Iris 50 Compass will probably find what looks like a small circle of metal super-glued to the compass card. This by now has probably turned a horrible green colour.

For such a nice to use and overall aesthetically pleasing compass I feel that this really lets it down.

I guess it is there to some how tune the compass but it really irritates me.

Other Iris 50s I have seen have had anything from a half circle to just over a full circle of metal glued to the card. It also seem like the superglue or what ever it is, is starting to eat its way across the rest of the card.

Do you think that this is some sort of design error and this piece of metal is there to correct it? Or an afterthought to balance the card or tune it?

Other Iris 50 owners have you been able to live with it?

Please let me know what you think as it is eating me up and I am considering taking it back to the shop to change it for something else.

Nick

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[stephenh]

I have had one of these for nearly 10 years now and it's still as good as new.
Can't fault it.

How old is yours? + the others you have seen ?
Maybe there was a duff batch?

Stephen

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[peterb]

Is your piece of metal on the south side of the compass? That is, under the N of the inner circle?

I've looked at mine, and while I can't see any piece of metal, there is a crescent shaped mark.

I suspect that it is there to balance the card against the effect of dip. The earth's field isn't just horizontal; there's a vertical component as well, and in the UK the vertical component is almost twice as strong as the horizontal. The effect is to make the compass card want to tilt north side down. Most compasses like the Iris and the older Mini have to give the card some sort of out-of-balance effect to counter this. With the Mini it was done by putting the magnet bars slightly off centre; if you look underneath you can see them quite clearly.



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[microvise]

My compass and the others I have seen are about 2 weeks old. I think it could well be a duff batch as it was on special reduced to £39.99.

The offending mark can even be seen on the pictures of the compass on their website.

For a quick look goto www.microvise.com/images/iris.jpg

I have put an arrow pointing to the mark.

Nick

 

[microvise]

Yes I am pretty sure we are talking about the same mark. You can see the mark I am talking about at www.microvise.com/images/iris.jpg

I now get the idea why it is there. It’s just a shame that they hadn’t come up with a more elegant solution like putting the magnet bars off centre.

Nick


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[peterb]

The problem is that a hand bearing compass like this only works properly in the northern temperate latitudes. If you take it to the equator then there won't be any vertical magnetic component to offset the balance weight, and as a result the card will be tilted south side down. It gets even worse if you take it to southern latitudes, where the balance weight and the magnetic field would both be tilting in the same direction. Most compass manufacturers make two or three variants of their compasses: northern, southern and equatorial.

I suspect that the Iris design has a standard card, either without the balance weight (equatorial) or with balance weights added north or south of the pivot.

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