What does a "hash mark" with a number inside a duct run mean on a blueprint?

This is typically an indicator for a system duct segment identifier , a CFM indicator, or a cross-reference tag linking back to a specific detailed section view drawing sheet (e.g., Tag 4 refers to Detail View on Sheet M-502).

['This is typically an indicator for a system duct segment identifier , a CFM indicator, or a cross-reference tag linking back to a specific detailed section view drawing sheet (e.g., Tag 4 refers to Detail View on Sheet M-502).']

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Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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This is typically an indicator for a system duct segment identifier, a CFM indicator, or a cross-reference tag linking back to a specific detailed section view drawing sheet (e.g., Tag...

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what does a "hash mark" with a number inside a duct run mean on a blueprint?