Step 1: Recall Dhumapana.
Dhumapana is medicated smoking therapy administered through a specific instrument, the Dhumayantra
Step 2: Recall the classical dimension.
Classical texts specify the length of the Dhumayantra used for Prayogika, or therapeutic, Dhumapana
Step 3: State the measurement.
The prescribed length is 36 Angula
\[ \boxed{36 Angula} \]