Inaccurate altimeter on new Instinct Solar

What did the barometer read prior to your elevation calibration and what was the correct pressure at that time?  No one can help you without knowing both as they work together. If you calibrated to the correct elevation, but the pressure reading is wrong, the watch will assume both are correct and when the barometer adjust to the correct pressure, it will change the elevation reading accordingly.  Every .05 inHg is about 50 feet.  So, if you calibrate elevation to 600 feet and the barometer shows the pressure at 30.10 when it's really at 30.00 elevation will show you at 700 feet once the barometer corrects itself. 

But it is easier to know, and therefore easier to calibrate to elevation. But you are saying that is not good enough? What is a reliable way to calibrate both when out in the field?

Because both the altimeter and barometer can drift for several reasons, it's always best to calibrate both prior to each activity. I check on my phone what the current pressure is and I'm fortunate enough to have a weather station a half mile from my residence so the data is pretty accurate.  There are also websites you can check to get the correct elevation or pressure readings if you're going to do an activity in an unfamiliar area. 

But if I only know the elevation and calibrate that, then even if the pressure reading is not accurate, at least I will know the changes in pressure. Which is what I am after.

Why would the pressure auto calibrate midway through an activity throwing my altitude ready to a far off number. I wouldn't have access to a phone or a nearby weather station in this hypothetical. 

If the pressure is off prior to starting the activity and then starts to adjust to the correct value, it can confuse the watch and it may think the change was due to elevation gain/loss.  This can be a problem is the barometer is set to auto or altimeter mode. Wind gust can also make the altitude change because it's such a sudden change in pressure the watch again assumes it was due to a change in elevation. . 

Well I have to admit that your suggestions are confusing me. When you try to calibrate the Barometric pressure, the Instinct asks you for current elevation data. At no point can you enter atmospheric pressure data into the Barometer calibration. 

You can calibrate the altimeter and not the barometer.  You can go to calibrate the barometer, and as you found, it ask if you want to calibrate elevation. You can do so using GPS which can have an error off + or - 400 feet, or the wrong elevation can be set unintentionally, or you can enter it manually.  This is why I said it's important to calibrate both to the known correct values prior to starting an activity for the best results.

Here's a clip from Garmin's Support website. 

However, depending on the GPS signal strength, these elevations can be off by as much as +/- 400 feet.

But that contradicts suggestions you made in earlier posts. Twice you said to calibrate both Pressure and Elevation, which is not possible.

I think what you should be suggesting to people is to calibrate often to known elevations, and to turn off auto calibrations as that is most likely the cause of misleading or false readings in both Altitude and Pressure. Especially over longer periods of time left un-calibrated.

R L said:

Twice you said to calibrate both Pressure and Elevation, which is not possible.

Are you saying you can't calibrate the altimeter and barometer independently on the Instinct Solar?  I've owned several Garmin watches with barometric altimeters and I've been able to do so.  I don't own an Instinct Solar.  Was my assumption that both can be calibrated independently incorrect and I've been wasting your time? 

Yes you did. Mine and anyone who reads this thread. The correct solution to OP's issue is 

R L said:

to calibrate often to known elevations, and to turn off auto calibrations as that is most likely the cause of misleading or false readings in both Altitude and Pressure. Especially over longer periods of time left un-calibrated.