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← How AI Learns II: Neural Networks Intuition

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Lesson 4 of 11

Measuring one wrong

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8 min

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The caretaker's log has twelve days. Eight teach the rule. Four are kept back to test it.

Four days, split by the rule's line: two wait, two call.
Step 1 of 2
  1. Four days, split by the rule's line: two wait, two call.
  2. One kept-back day breaks the pattern. Rule: wait. Caretaker: call.

The rule

The missed count needs its denominator. It comes from a real walk over the kept-back days.

The denominator is the total you count out of. Here it is 4. Go through the four kept-back days one by one. Ask the rule about each day. Add one when the rule and the caretaker's word disagree.

The rule missed 2 of the 4 kept-back days.

One miss is gauge 6, days 0. The tank fell six steps, even after a morning fill. The caretaker called. Gauge: 6 × 6 = 36. Days: 0 × 4 = 0. The sum is 36 + 0 = 36, under the threshold. The rule said wait. The other miss is gauge 5, days 3. Gauge: 5 × 6 = 30. Days: 3 × 4 = 12. The sum is 30 + 12 = 42, so the rule calls. The caretaker waited.

A count without its denominator cannot be judged. Missed 2 of 4 and missed 2 of 40 are different claims.

Move the two weights below. Watch the counts change.

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