Which of the following is a common threshold symbol used in audiometry?

In audiometry, threshold symbols are standardized notations used on audiograms to represent the results of hearing tests for each ear at various frequencies. The symbols "X" and "O" are commonly used to denote different thresholds for the left and right ears, respectively.

The "X" symbol is typically used to mark the air conduction thresholds for the left ear, while "O" represents the air conduction thresholds for the right ear. This convention allows audiologists and hearing specialists to clearly visualize and differentiate hearing ability in each ear at various frequencies.

The symbol "Δ" (delta) does not represent a common threshold in audiometry practices; it is not utilized to indicate hearing levels.

Thus, the answer encompasses both "X" and "O" as valid symbols that are frequently used in audiometric evaluations, confirming that both these symbols are integral for documenting and communicating hearing test results effectively.