What the Letters Actually Mean (Without the Confusion)
Many people searching for a Silva Arc Jet compass wonder what the letters S, C and 360 mean.
“Why does this one say S… this one C… and this one 360?”
And honestly, it looks more complicated than it really is.
Silva has a very good range of thumb compasses for orienteering, but the names can make people think there are huge differences between them. If you’re still deciding which type of compass suits you best, see our guide on how to choose an orienteering compass. In reality, the letters simply describe a few features.
Once you know what they stand for, the whole thing becomes quite simple.
All the compasses we are talking about here are from the Arc Jet range made by Silva.
They are all thumb compasses designed for orienteering, and they are all used in races.
The letters just explain what version you are holding
What does "S" mean - Spectra
If you see S in the name it means Spectra.
Spectra refers to the colour graphics printed on the compass dial.
At first glance this may seem like a different design, but there’s actually a reason for it.
When you run through the forest, you don’t waste time studying the compass. Most of the time you just glance at it while moving. Spectra lines make it easy for your eye to immediately recognize direction.
For some runners it really helps. Direction emerges quickly and you confirm your bearing without hesitation.
Other runners prefer the clean look of a simple dial. It really depends on personal preference and what your eye is comfortable with.
So the S doesn’t mean better compass – it just means Spectra dial graphics are included.
What the “C” Means – Compact
The letter C stands for Compact. This one is very straightforward.
It simply means the compass base is designed for smaller hands.
That’s it.
Some orienteers, especially juniors or runners with smaller hands, find the standard thumb compass slightly large. The Compact version sits more naturally and feels better balanced on the thumb.
If the normal Arc Jet feels comfortable to you, there is no reason to change to the Compact version.
But if you try one and it feels oversized, the C version can make a real difference in comfort.
What the “360” Means – Rotating Capsule
The Arc Jet 360 is the model with a rotating capsule.
Most Arc Jet compasses have a fixed capsule. The needle moves of course, but the housing itself does not rotate.
With the 360 version, you can rotate the capsule fully.
Why would someone want that?
This is closer to how a traditional compass works. Being able to set direction manually on the compass. In open terrain especially, this can be useful.
At the same time, many runners never rotate their capsule at all. They simply keep the compass aligned with the map and run.
So again, it is not about one being better than the other. It is just about navigation style and personal preference.
Quick Summary: Arc Jet Compass Differences
If you’re just trying to quickly understand the model names:
Arc Jet – Standard thumb compass.
Arc Jet S – Includes Spectra dial graphics to help read direction faster.
Arc Jet C – Compact version designed for smaller hands.
Arc Jet 360 – Includes a rotating capsule for taking bearings.
Right or left thumb
All Arc Jet compasses are available in right or left thumb versions.
It depends on which hand you hold the map.
Most right-handed runners tend to wear the compass on the left thumb and hold the map.
But people do it in another way too.
What matters is how you use it with the map – not just which hand you write with.
👉 If you’re not sure which one you need, we’ve explained it properly here:
“How to Choose an Orienteering Compass (Beginner to Advanced orienteering compass guide)”
Why do names cause so much confusion?
The truth is that the letters themselves don’t explain much.
If you don’t already know that C stands for compact or S stands for spectra, the names seem a little mysterious.
That is why people often feel uncertain while choosing a compass.
But once you understand what those letters mean, the choice becomes much easier.
You just decide what matters to you:
Small size, Spectra dial graphics, or a rotating capsule.
Everything else about the compass remains the same.
You can see the full range of Silva thumb compasses in our Arc Jet compass collection.
One More Thing Worth Knowing
While we’re talking about compasses, there is another topic that has started coming up more often in recent years.
Modern life is full of electronics — phones, car keys, GPS devices, speakers and all sorts of magnetic or electrical fields. Most of the time we don’t think about them at all.
But compasses do.
Every so often someone brings a compass to us and says something like “this thing is acting strange.”
At first glance it looks perfectly fine. The needle moves, nothing is broken, the capsule is clear. But when you check it properly, you realise the direction is simply wrong. North isn’t where it should be.
What usually happened we’ll talk a bit more about this in the next article, because it’s one of those things that most people never even think about — right up until the moment their compass starts pointing the wrong way.
Frequently Asked Questions
What does S mean on a Silva compass?
The letter S stands for Spectra.
This refers to the coloured dial graphics that make it easier to recognise direction quickly while running.
What does C mean on a Silva Arc Jet compass?
C stands for Compact.
This version has a smaller base and is designed for runners with smaller hands.