The 99.2% That Names the Real Design Lever

The 99.2% That Names the Real Design Lever

Ada re-derives this chapter’s own numbers step by step, at full precision

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Ada ADA · CALCULATION AUDIT

The 99.2% That Names the Real Design Lever

A glucose-monitoring smart lens takes 216 readings and 36 NFC bursts across an 18-hour wear, and the chapter totals the whole day at just 32.7 mJ. Its key insight is startling: the parts a designer instinctively optimises — sensing and the radio — barely register, because MCU sleep current alone is 99.2% of the budget. So what does that 99.2% figure actually name as the real design lever?

Companion to the chapter Smart Contact Lenses — every number here comes from that chapter.

See the relationship before changing it

The figure reads from left to right. The blue card is sleep power. The middle card applies the page rule. The green card is daily energy. Walk the arrows once: set the input, apply the rule, then read the result with its unit.

Sleep power changes daily energy An input card leads through the rule energy = (259.2 uJ active + sleep power x 64,800 s) / 1,000 to the daily energy result. INPUT PAGE INPUT APPLY THE RULE predict calculate check units OUTPUT RESULT
Walk the arrows. Sleep power dominates because it runs through the full eighteen-hour wear period.

Derive the baseline in four named moves

  1. 1

    Name the input. The chapter baseline is 0.5 uW.

  2. 2

    Name the relationship. energy = (259.2 uJ active + sleep power x 64,800 s) / 1,000

  3. 3

    Substitute with units. (259.2 + 0.5 x 64,800) / 1,000 = 32.66 mJ/day

  4. 4

    Read the result. Keep the unit beside the value. Use it only inside the technical boundary on this page.

Predict, then change sleep power

Try Predict the direction of energy = (259.2 uJ active + sleep power x 64,800 s) / 1,000. Test another sleep power, then compare daily energy.

0.5 uW
Chapter baseline
Daily energy

Observe Sleep power dominates because it runs through the full eighteen-hour wear period. Reset sleep power to 0.5 and compare daily energy.

Explain Sleep power dominates because it runs through the full eighteen-hour wear period.

Check yourself

What should you do before trusting a moved-control result?
Answer: Predict its direction, apply the shown relationship, keep the units, and reset to the worked baseline.
What does this small model leave out?
Answer: Only sleep power moves here. Field effects named in the technical boundary stay fixed.

Honesty note. This teaching model changes only sleep power. It is not a field prediction.

TryStart the lens budget with 216 sensor readings, 36 NFC bursts, and 18 hours of sleep, then select Check derivation.
ObserveThe daily total reports 32.7 mJ and attributes 32.4 mJ, approximately 99.2%, to MCU sleep rather than sensing or radio bursts.
ExplainSleep current controls the budget because it flows for 64,800 seconds, overwhelming the much higher currents that last only milliseconds.

Ada: The power-budget worked example ends on a striking claim: MCU sleep current is 99.2% of the lens’s daily energy. If that holds, it tells the designer exactly where to spend effort. Let me total the day from the chapter’s own component draws – 216 readings and 36 NFC bursts across an 18-hour wear.

  • Energy per reading: 2 x 0.15 + 12 x 0.05 + 1 x 0.01 = 0.30 + 0.60 + 0.01 = 0.91 uJ; sensing total 216 x 0.91 = 196.56 uJ.
  • Energy per burst: 30 x 0.05 + 12 x 0.02 = 1.50 + 0.24 = 1.74 uJ; transmission total 36 x 1.74 = 62.64 uJ.
  • Sleep energy: 0.5 x 18 x 3600 = 32,400 uJ.
  • Day total: 196.56 + 62.64 + 32,400 = 32,659.2 uJ, i.e. 32.7 mJ, at an average of 32,659.2 / 64,800 = 0.50 uW.
  • Sleep share: 32,400 / 32,659.2 = 0.992063, which rounds to 99.2%.

The whole example checks out. The design meaning is that sensing and radio – the parts a designer instinctively optimises – together sit under 0.8% of the budget, so halving the 150 ms sensor window saves almost nothing, while a 10x lower sleep current cuts total energy nearly 10x; the arithmetic is what redirects effort from the visible active path to the invisible sleep-current leak.

Technical boundaries
The lens power ledger deliberately does not simulate regulator efficiency, leakage outside MCU sleep, battery discharge curves, temperature, NFC coupling variation, harvesting, or safety limits; it integrates the stated sensing, burst, and sleep energies only.

Work the audit first, then check the displayed derivation.

Every number above is taken from the chapter’s own material and re-derived step by step.