# Completed demonstration example — conservatory lift

This alternate mechanism uses an 18-tooth driver, different turn requirements and a 270-degree cam.

## Causal model
Input rotation → external gear pair → cam → spring-return follower → lift output. The interlock blocks cam adjustment until released. Motion also requires the spring and specified cam phase.

## Prediction and diagnosis
For three output turns from five input turns: follower = 18 × 5 ÷ 3 = 30 teeth. The driven gear turns opposite the driver. A correct ratio did not initially produce a ready mechanism because the interlock was engaged and the return spring absent.

I released the interlock, set the cam to 270 degrees and attached the spring. I retained the ratio calculation because it was not contradicted by the readiness fault.

## Verification
Five input turns produced three opposite output turns. Both the amount and direction matched the prediction.

## Transfer
The changed task required two output turns from four input turns. I selected 36 follower teeth: 18 ÷ 36 × 4 = 2. The cam and spring conditions remained valid.

## Reflection
The useful distinction was between an incorrect transmission ratio and a blocked dependency. Changing gears would not have released the cam. In a new apparatus I would record the output requirement, list readiness conditions and test both separately.

Named output: mechanism-diagnosis. This is a model, not a real lock or physical qualification.

## Method to carry forward

Separate a wrong ratio from blocked movement with a discriminating test.

The assigned driver, readiness state and changed output differ. Inspect the state before copying a sequence of repairs.

The complete example explains one defensible approach. In your own challenge, select observations and tests from the supplied rules, keep your prediction separate from the result, and justify both the checks you perform and those you omit.