What people use the notebook for

Before investing time

Check an idea before you build on it

Situation

You read about a rule and want to know whether it is worth weeks of study.

What you end up with

A short, honest record of where the idea holds up in sample conditions and where it does not.

In the notebook

1. Write the rule as a hypothesis with a failure criterion
2. Run it on all four scenarios with default costs
3. Note which regimes help or hurt it

Read: from idea to testable hypothesis

Costs

Find the cost level where an edge disappears

Situation

A strategy looks good before costs and you suspect fees and slippage change the picture.

What you end up with

The approximate cost at which the sample result turns negative — a number to keep in mind for any real-world plan.

In the notebook

1. Save a run at 0 bps
2. Repeat at 5, 10 and 20 bps per fill
3. Compare net results in the run table

How costs are modelled

Market context

See how a signal changes meaning across regimes

Situation

A signal worked in one stretch of a chart; you want to know if that was the market rather than the rule.

What you end up with

A note that separates “the rule works” from “the market was kind”.

In the notebook

1. Keep the rule fixed
2. Run each scenario once
3. Write down the regime where it fails

Read: why context changes a signal

Research practice

Keep a research journal you can audit later

Situation

You test many variations and lose track of what you tried and why you dropped it.

What you end up with

A dated trail of hypotheses, runs and decisions — including the ones that failed.

In the notebook

1. One note per hypothesis
2. Write the conclusion after each batch of runs
3. Export to Markdown for your own archive

Read: building a research journal