CHAPTER 07 VISUAL LAB - Trace assignment and a stale result
Book boards: 07a and 07b

PRACTICE ROUTINE
Cover the board answer. Predict aloud, try the example, compare with the
stated result, change one input, and try again. Explain a discrepancy
before changing another thing. All marketing examples are fictional.

Use boards 07a and 07b. Open walkthrough.py in Thonny's editor and press F5.
Use the editor and output area together; no terminal is needed at this stage.

EXPECTED OUTPUT
EUR per enquiry: 25.0
After changing enquiries: 25.0
After recalculating: 20.0
Quoted name: rate
Stored value: 20.0

FOLLOW THE CODE
The first calculation stores 25.0 under rate. Assigning 15 to enquiries
changes that input name, but does not rerun a past division. The later rate
assignment explicitly recalculates and replaces the result with 20.0.
The quoted word rate is text. The unquoted name rate retrieves its value.

CHANGE, PREDICT, CHECK
In my_walkthrough.py, change the second enquiry assignment from 15 to 20.
Predict all outputs before running.
Answer: the first two numeric results stay 25.0. After recalculating, the rate
is 15.0; the final Stored value line also shows 15.0. Quoted name stays rate.

EXPLAIN THE TRACE
Write cost, enquiries and rate in three paper columns. After every assignment,
write their current values. A calculation reads the values available when
that line runs. Compare with python/chapter07.py for the fuller campaign,
percentage and rounded-total example; the same assignment rule applies.
