Arithmetic error: off by 10x in basis points calculation

Bug

Claude (Opus) made a decimal place error in a trivial arithmetic calculation, producing an answer off by exactly 10x.

Steps to reproduce

Ask Claude to calculate the loss in basis points for a deposit of 100,000 that returns 99,915.

Expected

(100000 - 99915) / 100000 * 10000 = 8.5 bps (0.085%)

Actual

Claude returned 0.85 bps (0.085%) — the percentage was correct, but the conversion from percentage to basis points was wrong by a factor of 10 (0.085% = 8.5 bps, not 0.85 bps).

When corrected by the user, Claude initially agreed with the right answer but still showed the wrong formula (85/100000*10000=8.5 was the user's correction).

Notes

• This is a model-level arithmetic issue, not a CLI bug
• The error pattern: correct intermediate result (0.085%) but wrong unit conversion (% → bps)
• Model: claude-opus-4-6