The method for calculating temperature depends very much on what you are using to measure the temperature. Thermocouples have a non-linear response and it is therefore not possible to use a formula for the calculations. When using the TC-08 unit this is done automatically by the software using a look-up table method.
If you can supply me with some more information as to what sensors you are using then I will be able to advise you further.
I am interested in doing this also (I emailed you about the ADC-11, you suggested the TC-08).
If I buy a temperature sensor from you can you supply the lookup values? Can you suggest one that would yield the best resolution over a 20-120° C range?
I guess this is a hint that perhaps you still have a market for signal conditioners.
Unfortunately we are unable to recommend a sensor to use. You will need to find one yourself, this should fit as well into the input voltage range as possible to maximise resolution.
As we cannot recommend a sensor we are therefore also unable to supply look up table information.