How does Medicare calculate payment for PT codes when it is secondary?

The rule, word for word

“(a) Services for which CMS pays on a Medicare fee schedule or reasonable charge basis. The Medicare secondary payment is the lowest of the following: (1) The actual charge by the supplier (or the amount the supplier is obligated to accept as payment in full if that is less than the charges) minus the amount paid by the primary payer. (2) The amount that Medicare would pay if the services were not covered by a primary payer. (3) The higher of the Medicare fee schedule, Medicare reasonable charge, or other amount which would be payable under Medicare (without regard to any applicable Medicare deductible or coinsurance amounts) or the primary payer's allowable charge (without regard to any deductible or co-insurance imposed by the policy or plan) minus the amount actually paid by the primary payer. (b) Example: An individual received treatment from a physician for which the physician charged $175. The primary payer allowed $150 of the charge and paid 80 percent of this amount or $120. The Medicare fee schedule for this treatment is $125. The individual's Part B deductible had been met. As secondary payer, Medicare pays the lowest of the following amounts: (1) Excess of actual charge minus the primary payment: $175−120 = $55. (2) Amount Medicare would pay if the services were not covered by a primary payer: .80 × $125 = $100. (3) Primary payer's allowable charge without regard to [...]”

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