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Re: how accurate is the barometer and the thermometer?

Casios can be precise, provide one take care and calibrate often.
Totally agree. After getting some real field experience and just wearing every day, my PRW5100 is extremely accurate. Just like any precision tool, you need to know how to use it and calibrate it to get the best results. Altitude is derived from pressure, and the pressure sensor in this model is very, very good with excellent thermal compensation. (note, I don't speak to the effectiveness of other modules, but the question was about protreks in general)

First you must start with a known altitude, or a starting reference point. From there, you can measure the change in altitude relative to that point, accepting that you're also factoring in changes due to weather conditions. The latter part is very important and affects all pressure-based altitude calculations equally, including the Suunto (they do offer more features such as enhanced reporting resolution and conveniences such as altitude lock, but do not have more inherent accuracy in the sensor). So absolute accuracy depends greatly on how fast you are ascending/descending, vs how quickly atmospheric conditions are changing.

There's a good 1 hour walking loop around my neighborhood I take frequently and I've found the 5100 to track it very consistently and accurately. My house is at 100 ft elevation so I always calibrate to that when I start off, and set the recording speed to 5 second intervals, and reset the trip history. The loop takes me down to a nearby river that's about 20 ft above sea level and I will always get a reading of 20-40 feet (depending on how high the water is and how close I get). From there it's an ascent up to about 200 feet, I get readings at the 180-200 mark. There are sections with smaller elevation changes, those under 20 feet get washed out in the resolution but in general it's very good at tracking the larger trending changes.

I do wish the resolution is better, but really only because I believe the sensor to be capable of more accuracy than was engineered in the scale (probably for sake of user friendliness and to err on the side of more stable readings). An interesting thing is the scale of altitude vs pressure: in Baro mode you're limited to seeing changes of 0.05 inHg, but in Alt you can measure 20 feet changes, which works out to about 0.025 change in inHg (I have not worked out the conversions between all the different options in meters vs feet, inHg vs bar etc to figure out which "scale" is the most granular, but it will probably bug me now to figure it out). So, if you REALLY care about tracking the pressure and you're in a fixed location, you can actually get more information out of the altimeter mode than you can the barometer! Plus, some nifty logging features and the history options. If you cared and wanted to do the conversions.
 
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