## TL;DR
Check for a unit change before investigating fraud or bugs: a distribution check that alarms after a currency change is seeing every amount double because values are now recorded in a different currency or unit, so normalise to one currency in the check. A distribution check compares raw numbers. When the unit behind the numbers changes, the distribution doubles overnight even though the business activity is identical.

```text
distribution check alarms after currency change doubles all amounts failure
```

## Use this when
- The check or run fails with this symptom: a distribution check alarms after a currency change doubles all amounts.
- You are working on a distribution or mean check over monetary amounts in a system that changed reporting currency or unit and the failure repeats on the same data or configuration.
- You need the failing rows, rule, or stage isolated before changing thresholds or code.

## Not for this skill when
- A real price increase that doubled amounts legitimately, where the check should be rebaselined after review rather than normalised.
- The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

## Steps
1. Verify the mean and total for the amount column before and after the change date. Verify: both roughly doubled at the same date
2. Confirm the currency or unit change and its effective date from the source system. Verify: the change date matches the alarm date
3. Check whether a currency column or an exchange rate table exists to normalise with. Verify: the normalisation inputs are available
4. Rewrite the check to compare amounts converted to one currency, or split the baseline at the change date. Verify: a replay over the change window shows no alarm
5. Annotate the metric history with the unit change. Verify: future investigations see the break explained

## Variant phrasings
### distribution check alarms currency change doubles amounts
The shorter phrasing focused on the named failure.
### column mean doubled after currency change failure
The symptom phrasing a searcher tries next.
### distribution drift currency unit change fix
The variant naming the failing stage or tool directly.

Compatibility: Soda and Great Expectations distribution checks, Monte Carlo distribution monitors over monetary fields

## Why it happens
Currency redenomination, a switch from units to thousands, or a new reporting currency changes the scale of every value at once. Distribution checks trained on the old scale see a population that no longer exists and alarm correctly against their baseline.

## Edge cases / pitfalls
- Mixed currency rows during a transition period break both raw and naive converted checks; handle the transition window explicitly.
- Doubling is suspiciously round; a factor near two, one hundred, or one thousand almost always means units, not behaviour.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_1C05AQwfaPEyj0C_sDWohA