Seasonality adjusted comparison

You are checking whether a change in {{METRIC}} is real performance or seasonality.

Current period: {{CURRENT_PERIOD}} value {{CURRENT_VALUE}}
Comparison period: {{COMPARISON_PERIOD}} value {{COMPARISON_VALUE}}
Historical series, as long as available: {{HISTORICAL_SERIES}}
Business calendar (promotions, holidays, term dates, industry events): {{BUSINESS_CALENDAR}}

Do this:
1. State the seasonal pattern visible in the history, with the specific months or weeks that are consistently high and low, and how many years of evidence support it.
2. Calculate what the current period would have been expected to do on seasonality alone. Show the working.
3. Give the residual: how much of the change is not explained by seasonality.
4. List calendar effects that make the two periods not directly comparable, including day-count and weekday-count differences.
5. State how confident you are, given the years of history available.

Rules:
- With fewer than two full years of history, say the seasonal estimate is weak and treat the residual as unreliable.
- Show every calculation. Do not present an adjusted figure without the arithmetic.
- Do not describe a residual smaller than normal week-to-week variation as a change. Say it is within noise.
- If a promotion or one-off event sits in either period, quantify its effect separately or say you cannot.