Is a temper meter just a way to log and plot temperatures on a chocolate sample as it cools down?

Unless I'm missing something like added cooling, this sounds like a fairly trivial gadget. It seems all you would need is identical size containers (maybe disposable plastic cups), a controlled temperature environment, thermocouple and the data logger.

That would be less than $100 in parts, not thousands of dollars. What am I missing?

it measures the latent heat of crystallization - when liquids crystallize, or when crystals "melt" they either absorb or release heat.  A tempermeter measures the amount and time of this heat over a very specific cooling scenario, and then does some math for you to make the results usable.

I'd be the very first to sign up for 10 of these from you if you built one for $100 8-)

I also was thinking about why these tempermeters are that expensive. After some research i found this page a few years ago: soncodipaul.weebly.com/tempermeter.html
It shows a cheap build tempermeter, but no description. After I sent him an email he replied with some info. He mentioned that the biggest problem is in recording the exact temperature at the exact time. But he also mentioned that this could be fixed with the right equipment and coding (or "just" some detailed temperature/time measering equipment?)

It was two years ago and I lost the interest in building such thing..  But maybe you are interested in it, would be happy to see some plans of building a tempermeter buy yourself )

It seems like recording the exact temperature and time would be a trivial matter, all you need is a small micro controller and a thermocouple, logging at 1KHz with sub millisecond timing accuracy would be easy to do.

It looks like the commercial ones have a temperature controlled environment to measure the change in which again shouldnt be too hard to achieve using a PID controller and heating element.

As far as I can see in tempermeters we use:

1. Aluminium cup is filled with sample chocolate, this is placed in "cup holder", covered, temperature probe is inserted in the centre of the sample and test is started.

2. Tempermeter provides consistent cooling (by controlling the temperature of "cup holder" at +8C).

3. Temperature recorded by the probe is recorded as it the sample is cooled and solidified.

4. This data is plotted and analysed.

5. If chocolate is perfectly tempered and monocrystaline structure is formend during crystalisation time temperature curve will be: down, stay at constant temperature and down again (close to how it would look for freezeing water) and temper index will be calculated as 5.

6. Undertempered and overtempered chocolates produce different time temperature curves (there is no "stay at constant temperature" part of the curve).

7. We agree on acceptable temper index range and if sample tests show that chocolate is within the range we start production, keep testing through the day and adjust tempering settings (on tempering machine) if needed.

Making one yourself could be done. As the whole test takes 8 minutes no more than 3-5 recordings per second would be needed (maybe even less). Containers are aluminium coffe capsule cups. Consistent "cup holder" temperature can be achieved by flowing constant temperature water through the coil), large tank and basic cooling control system will achieve this. Probes, hardware and software can be easily done as Kevlarcoated above stated.

For somebody with knowledge and time this is not so complex.