iPhone built-in compass not that good?

my old dedicated Garmin GPS compass had the same problem – inaccurate and not repeatable

my Samsung S9 has a pretty good compass

if I look at my track with gaia, then I can see which direction I’m going.  Any GPS with a map and track

Rex, thanks for bringing up this topic. I’ve only casually used the 3D Compass app on my Samsung S9. I calibrated the compass per directions, rotating a vertical figure 8 while rotating my body 360 degrees in the horizontal plane. I placed the phone next to my dev. corrected Silva compass in a wooden table next to the sunroom windows. The arrows lined up exactly. I believe that calibrating the phone compass is critical. My phone was off 12 degrees before calibration.

I appreciate that a smart phone has a compass on it, but only as a backup or when I wasn’t planning on using one.  And I’ve used it on dark cloudy nights when I get turned around in the woods or a strange city.

But if I expect to be crashing around off-trail in the fog, then I’ bring a button compass on top of my trekking pole or a wrist-strap orienteering compass straping outside my parka on my wrist so I can look at it frequently while using no hands and no battery life to do so.

I calibrated the compass per directions

I did the same between each reading on my iPhone. I also set the compass setting to “True North.”

I also checked the iPhone compass’s Lat & Long readings. They are accurate within a couple arc minutes.

I did not check to see if magnetic north was accurate, mostly because I don’t care where magnetic north is.

How do you align the phone to that accuracy – arc minutes?

With a Brunton compass I used for geology class, there were two pieces of glass (?) that flipped up, with a line on them.  You could look through them and align the lines with some geological feature and get the angle pretty accurately

With a Brunton compass I used for geology class, there were two pieces of glass (?) that flipped up, with a line on them.  You could look through them and align the lines with some geological feature and get the angle pretty accurately

That was probably a lensatic compass.

I have no info on the iphone compass, but beware that the magnetic compass in the Garmin GPSMAP 66i  (the fanciest inReach device) is absolute junk.

My first 66i unit had compass errors that ranged between -35 and +31 deg, depending on which direction it’s pointing. This is after multiple, supposedly successful, calibrations,  and ensuring I was far from any magnetic interference.

After chatting with Garmin support, they had me return it to REI for a new unit.

The new 66i is better, but still has errors that range from -4 to +16 deg, still obviously horrible for off-trail navigation. (E.g., standing in the middle of dense forest, trying to figure out which way to proceed to follow a track on the screen. The unit will switch to a GPS-based compass when you’re moving, and it seems quite good because the GPS seems quite good, but that’s not too convenient when you’re hanging on to a 45 deg slope.)

So after two units, I’ve given up on expecting the 66i compass to be worth anything. I really just take the 66i as a backup for navigation using my phone, but in extreme cold, or extreme wet, or if my phone dies, the 66i will be relied on to get out and having a bad compass is an issue (although of course I have an analog compass along as well).

Incidentally, my old Samsung S7 android phone has compass errors on the order of plus/minus 2-3 deg, barely measurable in my testing method.

So the question is, how is it that the compass in the REALLY expensive Garmin GPSMAP 66i is WAY more inaccurate than the compass in an ancient Samsung phone??