Engineering reference

Built from the same data the ISKRIT calculators run on

Each page covers one method: the formula, the thresholds, a worked example with numbers, and a link to the calculator that does it.

• Measurement uncertainty calculator: GUM budget with Type A, Type B and expanded U
  Measurement uncertainty budget per the GUM: Type A from repeated readings, Type B from instrument error, reference certificate and resolution, combined uc, effective degrees of freedom and expanded U.
• Area from coordinates calculator: shoelace formula for survey plots
  Area of a plot from the coordinates of its corners: grid eastings and northings or latitude and longitude from a map. Square metres, hectares, acres, perimeter, worked example.
• Bearing and distance from coordinates: survey inverse calculator
  Grid distance, whole-circle bearing, quadrant bearing and back bearing between two points from their northings and eastings, plus coordinates from bearing and distance.
• Rotating shift patterns: covering the posts and balancing the hours
  How a continuous roster is built from posts and crews, why the hours only balance over a period rather than a week, and the rest rules that quietly decide the pattern.
• Calibration intervals: setting them, shortening them, defending them
  Where a calibration interval comes from, what an out-of-tolerance result obliges you to do about earlier measurements, and the register fields an auditor actually asks for.
• Turning an estimate into a bill of quantities that foots
  Why the schedule that bills a job should be built from the estimate that won it, what breaks when it is retyped, and the checks that catch a schedule which does not tie to the contract.
• Progress billing: percent complete, carry-forward and retention
  How a running total works line by line across billing periods, why retention is computed per line rather than on the total, and the money contractors lose by never billing the release.
• Checking claimed quantities: the design schedule and the survey
  Two independent checks on what a contractor claims, why a percentage agreed on a site walk is not evidence for earthworks, and how survey-derived volumes change the conversation.
• Pile capacity from CPT: how the LCPC method reads a cone trace
  How cone resistance becomes shaft friction and toe resistance, why the trace is averaged over a window around the toe, and what the method does with a thin dense layer.
• Driven and bored piles: why the same soil gives different capacity
  What installation does to the soil around a pile, how that shows up in the shaft and toe terms, and why substituting one pile type for another during construction is not a like-for-like swap.
• What belongs on a borehole log, and what quietly gets left off
  The elements a usable log carries, why the water record is the part most often lost, and how the same log serves the driller, the designer and the contractor pricing the job.
• Drawing a cross section: correlating layers between boreholes
  How layers are matched from one borehole to the next, what vertical exaggeration does to the reader, and the cases where a straight line between two logs is a guess dressed as data.
• From an AGS4 file to a laboratory summary: what the groups carry
  Which AGS4 groups hold the laboratory results, how a test is tied back to the sample and the borehole, and the mismatches that break a summary table before any calculation happens.
• Characteristic values: turning a set of test results into one number
  How many determinations a design value needs, how outliers are rejected, and why the confidence level moves the characteristic value further from the mean for strength than for density.
• Void ratio, porosity and saturation from one density test
  The three-phase relationships worked through on a real sample, why saturation above 100 percent means a bad number rather than a wet soil, and which input the result is most sensitive to.
• When one soil layer is really two: splitting geotechnical units
  How a unit is tested for homogeneity, what a high coefficient of variation actually indicates, and why a depth trend inside a unit is a reason to split it rather than to average it.
• ASTM D4254 minimum index density: procedure and Dr calculator
  ASTM D4254 minimum and D4253 maximum index density: what the tests give, relative density calculator from three dry densities, and what changed when ASTM withdrew both standards in 2025.
• Relative density Dr and density index Id are not the same number
  Two definitions in circulation, one symbol used for both, and a systematic gap of several percentage points. Where each comes from and which one your specification means.
• USCS classification step by step: ASTM D2487
  How a grain size curve turns into a USCS group symbol: the 50 % fines split, the gravel-sand comparison, the well-graded criteria and where Atterberg limits become mandatory.
• Cu and Cc: what the two gradation coefficients actually tell you
  Coefficient of uniformity and coefficient of curvature: formulas, the well-graded thresholds for sand and gravel, and why a high Cu alone does not mean well graded.
• Dual symbols in USCS: the 5 to 12 percent fines band
  Why soils with 5 to 12 percent fines get two symbols like SW-SM, how the pair is assembled, and what a dual symbol tells a designer that a single symbol would hide.
• EN ISO 14688-1 against USCS: two different size ladders
  Sand ends at 2 mm in Europe and at 4.75 mm in the American system, fines start at 0.063 versus 0.075 mm. What that does to a percentage table and to the resulting class.
• AGS4 file validation: what the rules actually check
  The AGS Data Format v4 rules a validator can enforce from the file alone: line structure, group order, mandatory PROJ and TRAN, data types, units and abbreviations, key links.
• AGS4 syntax: the five rules that break a delivery
  Unquoted fields, stray characters between commas, unescaped quotes inside a value and heading count mismatches. The line-level AGS4 rules, what triggers them and how to fix the file.
• ASTM D2435 oedometer test: from the curve to Cc, mv and Eoed
  One-dimensional consolidation: what the pressure-void ratio curve gives, the difference between the logarithmic compression index and the linear coefficients, worked with numbers.
• Converting oedometer modulus to Young’s modulus
  The elastic relation between Eoed and E, why the correction always reduces the number, what Poisson ratio to assume by soil type, and how large the error is if you skip it.
• EN ISO 17892-5 and ASTM D2435: where the two diverge
  Two oedometer standards that share a formula set but differ in loading increments, time criteria for a step, specimen requirements and what the report must contain.
• ASTM D1196 plate load test: modulus and subgrade reaction
  The rigid circular plate formula, why the American method drops the embedment coefficient, how the modulus of subgrade reaction is obtained and what plate size does to it.
• DIN 18134: Ev1, Ev2 and the compaction ratio
  The two-cycle plate test used across Europe for earthwork acceptance: parabolic fit, tangent modulus at maximum stress, and the Ev2 to Ev1 criterion with a worked example.
• Ménard pressuremeter modulus: ASTM D4719 and EN ISO 22476-4
  How the pressuremeter modulus is calculated from the expansion curve, why the mean cavity radius is used instead of the initial one, and the fixed Poisson ratio convention.
• Hydraulic conductivity from a pumping test: Dupuit calculator and formulas
  Hydraulic conductivity from a steady-state pumping test: Dupuit calculator for unconfined and confined aquifers, typical values for soils, the radius of influence and how a field test differs from a permeameter.
• Shewhart control chart constants: A2, A3, B3, B4, D3, D4, d2, c4
  The ISO 8258 table of control chart factors for subgroup sizes 2 to 10, what each constant multiplies, and the individuals chart constants 2.66 and 1.128.
• The eight out of control tests on a Shewhart chart
  Zones A, B and C, the eight pattern tests from ISO 8258, what each one detects, and why running all eight raises the false alarm rate.
• Repeatability and reproducibility limits: where 2.77 comes from
  The r and R limits of ISO 5725, the factor 2.77 at 95 percent confidence, what counts as repeatability conditions, and how the limits are used to accept or reject a pair of results.
• How rebar cutting plans are optimised: the cutting stock problem
  Why greedy cutting leaves material on the floor, what column generation adds, how kerf and reusable offcuts enter the arithmetic, and what a good plan actually minimises.
• Cutting waste in rebar fabrication: what percentage is normal
  Offcut waste against unavoidable loss, why the two are budgeted separately, what drives the number up, and how to read a waste figure quoted by a supplier.
• Rebound hammer calibration: why the factory curve is not enough
  What a rebound number actually measures, why every mix needs its own correlation, and the acceptance checks a calibration curve has to pass before strength can be read off it.
• Kerf and offcut: what a linear cutting plan has to account for
  Saw width, trim allowance and the threshold between reusable remnant and scrap, and how each of the three changes the number of stock lengths a plan needs.
• Earthwork volume from survey points: grid, TIN and cross sections
  Three ways to turn surveyed levels into cut and fill volumes, what each one assumes about the surface, and where they disagree on the same site.
• Fire load density: the formula, the calorific values and the traps
  How fire load density is computed from material masses, why net and gross calorific values differ, which area goes in the denominator, and when a benchmark table may stand in for a survey.
• Explosive atmosphere zones 0, 1, 2 and 20, 21, 22 explained
  What decides the zone number, how the grade of release maps onto it, why dust gets its own series, and the difference between the number of a zone and its extent in metres.
• Pollution charges per tonne: how the over-limit multiplier works
  Why a per-tonne pollution charge is never a single rate, how the permitted load, the temporary allowance and the excess are charged differently, and what the doubling and the 25 and 100 multipliers are actually for.
• The Russian environmental fee: who pays, when, and how the advances work
  Which facilities owe the negative environmental impact fee, the reporting calendar, the three permitted ways of computing a quarterly advance, and how the year-end balance settles against what was already paid.