| Clue | Length | Answer |
|---|---|---|
| Rule of thumb | 4 letters | norm |
| Rule of thumb | 5 letters | trial |
| Rule of thumb | 7 letters | r-and-d |
| Rule of thumb | 7 letters | testing |
| Rule of thumb | 8 letters | standard |
| Rule of thumb | 9 letters | guideline |
| Rule of thumb | 15 letters | trial-and-error |
| Rule of thumb | 24 letters | research-and-development |
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