This is an article about precision with judgment. The joke in the title is the trap itself. You cannot optimize the fifth decimal place if you have not even fixed the first digit. Use these rules to earn precision in the right order.

1) Name the first digit

State the order of magnitude first. Are we talking tens, thousands, or millions. If the scale is fuzzy, your fifth decimal place is fantasy.

2) Write the decision and the tolerance

What choice will this number influence, and how precise must it be to change that choice. Define acceptable error bands before you compute.

3) Use ranges, not points

Replace single numbers with low to high ranges and confidence levels. Ranges prevent the mind from polishing a guess into fake certainty.

4) Sample before census

Run a quick sample or pilot to expose reality at low cost. A small, cheap test often reveals the correct first digit immediately.

5) Instrument before you improve

Measure the system cleanly, then optimize. If your inputs are noisy or biased, additional decimals only decorate the error.

6) Price the next decimal

Estimate the time and money required for each extra digit of accuracy, and the expected value it returns. Stop when the next decimal is not worth its price.

7) Prefer reversible moves

Choose actions that can be undone or adjusted. When the door swings both ways, you learn faster and avoid overpaying for precision upfront.

8) Separate stakes from style

Ask whether an error of one whole digit would matter to safety, legality, trust, or profit. If not, ship the coarse version and learn.

9) Stage your modeling

Start with the simplest model that captures the main drivers. Add complexity only when it reduces error on new data, not on the dataset you trained on.

10) Validate assumptions directly

List the assumptions that generate your number. Test the riskiest one with a direct measurement or interview. One verified assumption can fix the first digit in minutes.

11) Set explicit stop rules

Timebox analysis and define exit criteria. Example: stop when the range narrows enough to pick an option, or when two candidate actions tie within tolerance.

12) Close the loop with feedback

Ship a decision, log outcomes, and compare predicted to observed. Calibration beats precision. Each cycle moves you toward useful accuracy where it counts.

A tiny checklist you can paste into any doc

Decision this number informs:
Required tolerance to change that decision:
Current best range and confidence:
Cheapest test to tighten the range today:
Assumption to validate first:
Stop rule for this round:
Next action and review time:

Start with the first digit. Earn each decimal with tests that move reality. Precision is a tool, not a trophy.