Just plugging it into a multi-meter will not tell you the temperature. The multi-meter will display the mv output of the TC. This will be only as accurate as the meter. Unless it is a calibrated lab type millivoltmeter, it will not work well. And then you would also need the output chart for the TC. It would give the mv/deg and some readings of the calibrating tests. You would have to do the math to know what the temperature was.
You will have to have an A to D converter and some sort of pre-programed reading device to display the temperature in degrees. That is what a PID does. A cheap one costs about $25.
"Reading up a little" is not going to get you ready to build a forge to do HT in. You need to understand both the operation principle and the construction of it. To know the actual temperature, you will need an accurate pyrometer. This can be bought or built. Understanding how they work and why the reading can be off is also necessary if you want good results. The way to get this knowledge is to read....not just a little or a few paragraphs....but a lot. There is a ton of good info in the stickies and on past threads covering these subjects. It may take a week or more to read ( and re-read) all that info, but when done and understood, most of your future questions will be answered by your own personal knowledge.
Reading and studying the principles of HT and how to do it for different steel types will also help you design and build your forge. Knowing what you want it to do is as important as knowing how to do it.
I know everyone today wants it all by tomorrow, but your forge build will be far better if you take a few weeks to learn the basics first. Personally, I would rather have a good forge in December, than a poor forge next week.
