Computed by stonks: nominal Henry Hub natural gas spot price (series henry-hub-natural-gas-price) deflated by US CPI-U (series us-cpi) to constant 2025 dollars. Real value = nominal × (2025 average CPI ÷ CPI at or before the observation date), CPI step-aligned (most recent monthly reading on or before each daily price date), never interpolated. Fixed 2025 base year.