Other key physicochemical parameters of raw CaO (particle size, particle porosity, presence of unoxidized calcium carbonate ''grit'', etc.) that result from variation in kiln calcination of limestone [29] (the industrial manufacturing process) also must be kept consistent for consistent heat profiles. However, we were able to produce precise heat profiles in our prototypes with commodity grades of CaO. This makes the only disposable materials (CaO, water, and PCR tubes) in the device very inexpensive. The reaction of CaO and water can be tuned somewhat to control the steepness of the temperature ramp and the maximum temperature for a given reaction chamber, although flexibility and precision is greatly improved by including the EPCM.