Which symbol is commonly used to denote "a change of" in measurements?

The symbol commonly used to denote "a change of" in measurements is the Greek letter Delta (Δ). In various scientific and engineering contexts, Delta represents the difference or change between two values. For instance, in physics and mathematics, Δx is often used to indicate a change in the variable x, such as a change in position or displacement. This notation is essential for conveying changes in quantities, whether it's temperature (ΔT), pressure (ΔP), or any other measurable quantity.

In contrast, the other symbols like Sigma (Σ), Gamma (Γ), and Phi (Φ) have specific meanings in different fields. Sigma is commonly associated with summation in mathematics and statistics, Gamma often denotes a specific type of function or rate in physics, and Phi usually relates to angles or the golden ratio in mathematics. Therefore, Delta is distinct in its role of representing change, making it the correct choice for this question.