lilernoEngineeringOpening Lilerno
Chapter 23 · Guided self-study
Intro + external course studyDefend a design decision using evidence and explicit trade-offs.
Build the idea
An original introduction, worked example and practice, followed by a curated reading sequence. The external courses supply deeper teaching and problem sets.
This guide is an orientation, not a complete university module. Practical work needs suitable facilities, safety review and supervision.
Start with these prerequisites
Shared science foundations
Engineering decisions affect people, resources and systems beyond the calculation. Make requirements, evidence, uncertainties and trade-offs explicit.
Module lens
Cost, maintenance and impact unfold over time; a single purchase price cannot represent the whole decision.
Cost, energy, reliability, maintainability and accessibility can conflict. State the system boundary and service conditions before comparing alternatives. A lower purchase price may hide maintenance or disposal costs.
Identify hazards, affected people, failure consequences and uncertainty. Prefer safer designs and qualified review over unsupported numerical safety claims. Standards and legal obligations must be checked for the real jurisdiction and application.
See the relationship
Change one quantity, watch the graph respond, then explain the result in your own words.
Predict → change → explain
At what service life does the more expensive option become cheaper overall?
Axes: Service life (years) → Total cost (currency units). Bounds may rescale when inputs change.
At 3 years: A = 160; B = 170 currency units.
Illustrative costs: A = 100 + 20/year; B = 140 + adjustable annual cost. No discounting, residual value or external impacts. Cost alone cannot select a design.
Original Lilerno illustration. Inputs are illustrative; this is not experimental evidence or a design rating.
| Series | Service life (years) | Total cost (currency units) |
|---|---|---|
| Option A | 0 | 100 |
| Option A | 0.125 | 102.5 |
| Option A | 0.25 | 105 |
| Option A | 0.375 | 107.5 |
| Option A | 0.5 | 110 |
| Option A | 0.625 | 112.5 |
| Option A | 0.75 | 115 |
| Option A | 0.875 | 117.5 |
| Option A | 1 | 120 |
| Option A | 1.125 | 122.5 |
| Option A | 1.25 | 125 |
| Option A | 1.375 | 127.5 |
| Option A | 1.5 | 130 |
| Option A | 1.625 | 132.5 |
| Option A | 1.75 | 135 |
| Option A | 1.875 | 137.5 |
| Option A | 2 | 140 |
| Option A | 2.125 | 142.5 |
| Option A | 2.25 | 145 |
| Option A | 2.375 | 147.5 |
| Option A | 2.5 | 150 |
| Option A | 2.625 | 152.5 |
| Option A | 2.75 | 155 |
| Option A | 2.875 | 157.5 |
| Option A | 3 | 160 |
| Option A | 3.125 | 162.5 |
| Option A | 3.25 | 165 |
| Option A | 3.375 | 167.5 |
| Option A | 3.5 | 170 |
| Option A | 3.625 | 172.5 |
| Option A | 3.75 | 175 |
| Option A | 3.875 | 177.5 |
| Option A | 4 | 180 |
| Option A | 4.125 | 182.5 |
| Option A | 4.25 | 185 |
| Option A | 4.375 | 187.5 |
| Option A | 4.5 | 190 |
| Option A | 4.625 | 192.5 |
| Option A | 4.75 | 195 |
| Option A | 4.875 | 197.5 |
| Option A | 5 | 200 |
| Option A | 5.125 | 202.5 |
| Option A | 5.25 | 205 |
| Option A | 5.375 | 207.5 |
| Option A | 5.5 | 210 |
| Option A | 5.625 | 212.5 |
| Option A | 5.75 | 215 |
| Option A | 5.875 | 217.5 |
| Option A | 6 | 220 |
| Option A | 6.125 | 222.5 |
| Option A | 6.25 | 225 |
| Option A | 6.375 | 227.5 |
| Option A | 6.5 | 230 |
| Option A | 6.625 | 232.5 |
| Option A | 6.75 | 235 |
| Option A | 6.875 | 237.5 |
| Option A | 7 | 240 |
| Option A | 7.125 | 242.5 |
| Option A | 7.25 | 245 |
| Option A | 7.375 | 247.5 |
| Option A | 7.5 | 250 |
| Option A | 7.625 | 252.5 |
| Option A | 7.75 | 255 |
| Option A | 7.875 | 257.5 |
| Option A | 8 | 260 |
| Option A | 8.125 | 262.5 |
| Option A | 8.25 | 265 |
| Option A | 8.375 | 267.5 |
| Option A | 8.5 | 270 |
| Option A | 8.625 | 272.5 |
| Option A | 8.75 | 275 |
| Option A | 8.875 | 277.5 |
| Option A | 9 | 280 |
| Option A | 9.125 | 282.5 |
| Option A | 9.25 | 285 |
| Option A | 9.375 | 287.5 |
| Option A | 9.5 | 290 |
| Option A | 9.625 | 292.5 |
| Option A | 9.75 | 295 |
| Option A | 9.875 | 297.5 |
| Option A | 10 | 300 |
| Option B | 0 | 140 |
| Option B | 0.125 | 141.3 |
| Option B | 0.25 | 142.5 |
| Option B | 0.375 | 143.8 |
| Option B | 0.5 | 145 |
| Option B | 0.625 | 146.3 |
| Option B | 0.75 | 147.5 |
| Option B | 0.875 | 148.8 |
| Option B | 1 | 150 |
| Option B | 1.125 | 151.3 |
| Option B | 1.25 | 152.5 |
| Option B | 1.375 | 153.8 |
| Option B | 1.5 | 155 |
| Option B | 1.625 | 156.3 |
| Option B | 1.75 | 157.5 |
| Option B | 1.875 | 158.8 |
| Option B | 2 | 160 |
| Option B | 2.125 | 161.3 |
| Option B | 2.25 | 162.5 |
| Option B | 2.375 | 163.8 |
| Option B | 2.5 | 165 |
| Option B | 2.625 | 166.3 |
| Option B | 2.75 | 167.5 |
| Option B | 2.875 | 168.8 |
| Option B | 3 | 170 |
| Option B | 3.125 | 171.3 |
| Option B | 3.25 | 172.5 |
| Option B | 3.375 | 173.8 |
| Option B | 3.5 | 175 |
| Option B | 3.625 | 176.3 |
| Option B | 3.75 | 177.5 |
| Option B | 3.875 | 178.8 |
| Option B | 4 | 180 |
| Option B | 4.125 | 181.3 |
| Option B | 4.25 | 182.5 |
| Option B | 4.375 | 183.8 |
| Option B | 4.5 | 185 |
| Option B | 4.625 | 186.3 |
| Option B | 4.75 | 187.5 |
| Option B | 4.875 | 188.8 |
| Option B | 5 | 190 |
| Option B | 5.125 | 191.3 |
| Option B | 5.25 | 192.5 |
| Option B | 5.375 | 193.8 |
| Option B | 5.5 | 195 |
| Option B | 5.625 | 196.3 |
| Option B | 5.75 | 197.5 |
| Option B | 5.875 | 198.8 |
| Option B | 6 | 200 |
| Option B | 6.125 | 201.3 |
| Option B | 6.25 | 202.5 |
| Option B | 6.375 | 203.8 |
| Option B | 6.5 | 205 |
| Option B | 6.625 | 206.3 |
| Option B | 6.75 | 207.5 |
| Option B | 6.875 | 208.8 |
| Option B | 7 | 210 |
| Option B | 7.125 | 211.3 |
| Option B | 7.25 | 212.5 |
| Option B | 7.375 | 213.8 |
| Option B | 7.5 | 215 |
| Option B | 7.625 | 216.3 |
| Option B | 7.75 | 217.5 |
| Option B | 7.875 | 218.8 |
| Option B | 8 | 220 |
| Option B | 8.125 | 221.3 |
| Option B | 8.25 | 222.5 |
| Option B | 8.375 | 223.8 |
| Option B | 8.5 | 225 |
| Option B | 8.625 | 226.3 |
| Option B | 8.75 | 227.5 |
| Option B | 8.875 | 228.8 |
| Option B | 9 | 230 |
| Option B | 9.125 | 231.3 |
| Option B | 9.25 | 232.5 |
| Option B | 9.375 | 233.8 |
| Option B | 9.5 | 235 |
| Option B | 9.625 | 236.3 |
| Option B | 9.75 | 237.5 |
| Option B | 9.875 | 238.8 |
| Option B | 10 | 240 |
| Chosen life | 3 | 160 |
| Chosen life | 3 | 170 |
Save your place when you finish reading.
Original Lilerno example
An illustrative option costs 100 currency units initially and 20 per year for 3 years. Ignore discounting and residual value.
Declare the simplified cost model.
Total = initial + years × annual cost.
100 + 3 × 20 = 160 currency units.
Test the model
Open learning, traceable sources
Work in this order. These links open the publisher’s material; free access does not always permit republication.
MIT OpenCourseWare · Spring 2009
Start with: Design process and project requirements
Review a design decision and add stakeholders, maintainability and failure consequences to its requirements.
NIST / SEMATECH
Start with: Reliability and experimental evidence
Distinguish an evidence-backed reliability claim from a small demonstration.
Recall, then record
Close the explanation and answer these in your own words. Return tomorrow, then again later in the week.
Who is affected?
Which costs or impacts are outside the boundary?
What needs qualified review?
Create a decision matrix with evidence for each rating, a hazard register and a list of unresolved questions. This is a starting brief, not a completed safety assessment.
Self-reported tasks, not an assessment of mastery or university credit. Reading a page does not complete a chapter.
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Open learning, traceable sources
Original Lilerno lessons and diagrams, supported by these references. Free access does not always permit republication. Links open the publisher’s material.
Measurement-process characterization, exploratory analysis, process modelling, quality and experimental design.
Linked reference. NIST-authored federal material and third-party contributions can have different rights; verify item notices before reuse.
Open source ↗Rights / publisher record ↗Mechanical design, mechanisms, and project thinking.
CC BY-NC-SA, except marked exceptions; external study only.
Open source ↗Rights / publisher record ↗