Thermodynamic scale in the S.I. system: select the correct unit of temperature used internationally for scientific and engineering work.

Introduction / Context:
Temperature scales appear everywhere in engineering: material properties, gas laws, and heat-transfer calculations. The S.I. chooses a single coherent base unit for thermodynamic temperature to ensure universal comparability and to avoid offsets that complicate equations.

Given Data / Assumptions:

• The S.I. base unit for thermodynamic temperature is the kelvin (K).
• Informal terms like “degree centigrade” are deprecated; “degree Celsius” (°C) remains widely used for everyday measurements but is not the S.I. base unit.
• Fahrenheit and Rankine are non-S.I.

Concept / Approach:
Many formulas (e.g., ideal gas law) require an absolute scale without arbitrary zero points; the kelvin provides this. While Celsius is convenient for weather or lab readings, kelvin is the fundamental unit in S.I.-based computations and standards.

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