Employers must provide annual audiograms within one year of the baseline. It is important to test workers’ hearing annually to identify deterioration in their hearing ability as early as possible. This enables employers to initiate protective followup measures before hearing loss progresses. Employers must compare annual audiograms to baseline audiograms to determine whether the audiogram is valid and whether the employee has lost hearing ability or experienced a standard threshold shift (STS). An STS is an average shift in either ear of 10 dB or more at 2,000, 3,000, and 4,000 hertz.