## TL;DR

European invoices write 1.234,56 where US invoices write 1,234.56, and misreading the convention shifts amounts by 100x. Determine the convention from the vendor country and the invoice's own formatting: the last separator before the final two digits is the decimal mark. Normalize to a canonical decimal representation before any arithmetic, and flag amounts where both readings are plausible.

## Error

```text
Extracted amount: 1.234 (ambiguous: 1234.00 US vs 1.234 EU)
```

## Steps

1. Take the vendor country as the prior: EU implies comma-decimal, US/UK implies point-decimal.
   Expected: A prior convention.
2. Inspect the invoice's own numbers: the separator before the last two digits is the decimal mark.
   Expected: Document-level evidence.
3. Normalize all amounts to canonical decimal form.
   Expected: Comparable numbers.
4. Run arithmetic validation on normalized amounts.
   Expected: Catches 100x errors immediately.
5. Flag any amount where both conventions produce plausible values.
   Expected: Human decides the ambiguous cases.

## When to use

- International invoices with ambiguous separators
- Amounts that look 100x too large or small
- EU vendor invoices in AP

## When not to use

- Single-convention vendor bases
- Currency symbol misreads
- Post-normalization arithmetic

## Compatibility

Extractor-agnostic; implement in the normalization layer before validation.

## Variant phrasings

### comma vs dot decimal invoice

### European number format invoice

### 1.234,56 parsing

## Root cause

Decimal conventions are cultural, and OCR reads the characters correctly while the meaning depends on locale. A single misassigned separator multiplies or divides the amount by a hundred.

## Edge cases

- Swiss invoices use apostrophes as thousands separators (1'234.56); include in patterns
- Some invoices mix conventions; document-level majority wins
- Indian numbering (lakh/crore grouping) needs its own pattern

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ubc0SfulWJ15NyWMIYa0dg