Preparatory Certificate cheat sheet

Input → process → output model: every system transforms defined inputs into measurable outputs under stated constraints; document all three before evaluating performance.

Accuracy vs. precision: accuracy is closeness to the true value; precision is repeatability among repeated measurements. A result can be precise and inaccurate (systematic bias).

Systematic error shifts all readings in one direction and is correctable by calibration; random error scatters around a mean and is reduced by averaging repeated trials.

Significant figures: the last digit is the uncertain one. Addition/subtraction keeps the fewest decimal places; multiplication/division keeps the fewest significant figures.

Unit consistency is mandatory before any calculation: convert to one coherent system (e.g., SI base units) and carry units through every step as a check.

A control is a known reference run alongside the unknown; a blank contains everything except the analyte. Controls detect bias, blanks detect contamination.

Cause-and-effect requires a controlled comparison; correlation alone does not establish causation because a third variable may drive both.

Scale and proportion: linear relations change by a constant difference, exponential/logarithmic relations by a constant ratio; plot data before assuming linearity.

Sensitivity = change in instrument response per unit change in the measured quantity; it is a slope, not a measure of correctness.

Limit of detection (LOD) is the smallest amount distinguishable from blank at a stated confidence; limit of quantification (LOQ) is the smallest amount measurable with acceptable precision.

Tolerance is the total permitted variation (upper minus lower limit); bias is the signed difference between the mean result and the reference value.

Calibration is the act of relating instrument readings to reference values; verification is confirming an item still meets its specification; validation is documented proof a method suits its intended use.

Resolution is the smallest distinguishable increment of a display or measurement; it bounds but does not guarantee accuracy.

Repeatability = same operator, same equipment, short time; reproducibility = different operators, equipment, or laboratories.

Nominal value is the designated target; actual (true) value is the reference-determined value; indicated value is what the instrument shows.

Uncertainty is a quantified interval about a result, expressed as a standard uncertainty or an expanded uncertainty with a coverage factor k.

Conservation laws (mass, energy, charge) set the balance equations used to check any process: inputs minus outputs equals accumulation.

Ohm's law V = I × R and power P = V × I underpin electrical measurement; a voltmeter is placed in parallel, an ammeter in series.

Proportionality and the linear model y = mx + b: slope m is sensitivity, intercept b is the offset; a nonzero intercept signals a systematic offset.

Heat transfer by conduction follows rate ∝ (area × temperature difference)/thickness; convection and radiation dominate where conduction paths are absent.

Equilibrium: a system at steady state has constant measured values even while material or energy flows through it; equilibrium requires no net flow.

Feedback: negative feedback reduces deviation and stabilizes output; positive feedback amplifies deviation and can drive runaway behavior.

Measurement chain theory: each element (sensor, transducer, amplifier, display) contributes its own error; total uncertainty combines them, not just the largest.

Sampling theorem: to capture a signal faithfully, sample at more than twice the highest frequency present, otherwise aliasing folds high frequencies into false low ones.

Standard operating procedure order: prepare and check equipment → calibrate with traceable references → run blank/control → measure sample → record → clean and store.

Calibration sequence rule: use at least three points spanning the working range, bracket every sample between standards, and re-verify with an independent check standard.

Replication: run at least duplicate measurements; report the mean and the spread. A result outside control limits triggers investigation before any new data is accepted.

Change one variable at a time in an experiment; if multiple factors interact, use a designed experiment (factorial) rather than one-factor-at-a-time.

Titration endpoint is detected by indicator or instrument inflection; the equivalence point is theoretical and is estimated from the curve, not read directly.

Gravimetric and volumetric workflows require temperature equilibration of glassware and solutions, because volume and density vary with temperature.

Troubleshooting order: verify power and connections → verify calibration status → check consumables/reagents → check environment → escalate with recorded evidence.

Documentation must be contemporaneous and attributable: record raw data, conditions, instrument ID, and any deviation at the time it occurs, never from memory.

Choose an instrument whose range brackets the expected value and whose resolution is at most one-tenth of the tolerance being checked (rule of ten).

A multimeter's accuracy spec is often given as ±(% of reading + counts); convert counts to absolute units before combining with the percentage term.

Balances: level the instrument, zero or tare, and allow warm-up; eccentric loading error is checked by placing a test weight at different pan positions.

Glassware classes: volumetric flasks and pipettes are calibrated to contain (TC) or to deliver (TD); a graduated cylinder is for approximate volumes only.

Thermometers and sensors require immersion depth and response-time awareness; a slow sensor lags rapid changes and under-reports peaks.

Pressure gauges should be selected so normal operation falls in the middle third of the scale; readings near the ends carry the largest relative error.

Reference standards must be traceable to a national or international standard and must be recertified on a defined interval.

Preventive maintenance schedule: inspect, clean, verify against a check standard, and record; drift between verifications indicates the need for recalibration.

Hierarchy of controls, most to least effective: elimination, substitution, engineering controls, administrative controls, personal protective equipment.

Safety data sheet sections cover identification, hazards, composition, first aid, firefighting, accidental release, handling/storage, exposure controls, and disposal.

Personal protective equipment is the last line of defense: select eye, hand, body, and respiratory protection from the assessed hazard, not from habit.

Electrical safety: de-energize and lock out/tag out before servicing; verify absence of voltage with a tested instrument; treat unknown conductors as live.

Chemical storage segregates by hazard class (oxidizers away from flammables, acids away from bases); containers stay labeled with contents and hazard.

Ethical practice: report data as measured, disclose conflicts of interest, preserve records for the required retention period, and never alter another person's record.

Standards conformity: an accredited laboratory operates a quality management system with documented methods, traceability, internal audits, and corrective action for nonconformities.

Incident response order: protect people, stop the hazard, contain the spill or release, notify per protocol, then document and investigate root cause.