Final answer:
The best method to determine a chiller's normal charge for leak rate calculations should come from manufacturer specifications or the system's maintenance history; none of the provided options directly answer this question.
Step-by-step explanation:
The best method to determine a chiller's normal charge for leak rate calculations is not listed among the options provided. However, to manage and identify leaks, one would typically use a refrigerant leak detector. Leak rate calculations based on normal charge would usually reference manufacturer specifications, service documentation, or rely on the maintenance history of the system to establish a baseline charge amount. Using a pressure-temperature chart can help in understanding the conditions of the refrigerant but is not directly used to determine the charge. A refrigerant recovery machine is used to remove refrigerant from a system, not calculate normal charge. Lastly, a refrigerant charging scale can weigh the refrigerant being added or removed but does not itself calculate the normal charge.
For leak rate calculations in other contexts, such as a spectrometer's role in detecting leaks in a research apparatus, the spectrometer is used to detect and quantify minuscule amounts of leaking substances like helium.