Learn one useful thing today.
NAREIT FFO, AFFO & True Dividend Payout Ratio Formula
Calculate Equity REIT NAREIT Funds From Operations (FFO), Adjusted Funds From Operations (AFFO) After Straight-Line Rent Accruals and Recurring TI/LC Maintenance Capex, Headline FFO Payout Ratio, and True Cash AFFO Payout Ratio.
Read the guide →Underground NATM Support & Ground Control, Shotcrete Rebound & Rockbolt Wedge FactorNATM Shotcrete Rebound Delivery & Rockbolt Safety Formula
Calculate In-Place Crown Shotcrete Volume (m³), Rebound-Adjusted Batch-Plant Delivery Volume (m³), Tributary Dead-Weight Rock-Wedge Load per Bolt (kN), and Rockbolt Factor of Safety.
Read the guide →Heat Transfer, Electronics Thermal Management & Passive Natural ConvectionNatural Convection Rayleigh & Churchill-Chu Nusselt Formula
Calculate Vertical Heatsink / Enclosure Plate Laminar Rayleigh Number Ra_L, Exact Churchill-Chu Laminar Nusselt Number Nu_L in Air (Pr = 0.71), Natural-Convection Heat-Transfer Coefficient h (W/m²·K), and Passive Heat Dissipation Q (W).
Read the guide →High-Voltage Transmission & Substation Duct Banks, NEC 310.15(C) Neher-McGrath AmpacityNeher-McGrath Underground Cable Ampacity Formula
Calculate AC Skin/Proximity Conductor Resistance Rac (mOhm/m), Available Conductor Thermal Headroom (K), Maximum Continuous Ampacity Imax (A), and Joule Heat Load (W/m).
Read the guide →Statistical AnalysisNelson-Aalen Cumulative Hazard H(t), Aalen Variance & Fleming-Harrington Survival
Estimate nonparametric cumulative failure hazard H(t) = SUM(d_i / n_i), Aalen standard error SQRT(SUM(d_i / n_i^2)), and exponential survival S_FH(t) = EXP(-H(t)) on right-censored cohorts.
Read the guide →Financial ModelingNelson-Siegel Yield Curve Model: Level, Slope & Curvature Spot & Forward Rates
Fit parsimonious sovereign and corporate spot yield curves across any maturity tau using Charles Nelson and Andrew Siegel’s (1987) four-parameter level, slope, and medium-term hump loadings.
Read the guide →Financial ModelingNelson-Siegel-Svensson (NSS) 4-Factor Yield Curve & Second Curvature Hump
Extend 4-parameter Nelson-Siegel with Lars Svensson’s (1994) second curvature loading beta_3 and decay tau_2 used by the ECB and Bundesbank to fit 10Y–30Y sovereign convexity.
Read the guide →Marketing Science & Industrial OrganizationNerlove-Arrow Advertising Goodwill Stock Formula
Generalize Dorfman-Steiner to durable brand equity dG/dt = a - delta*G using Marc Nerlove and Kenneth Arrow’s (1962) dynamic goodwill-to-sales rule G* / (P*Q) = beta_G / (epsilon_P * (r + delta)).
Read the guide →EngineeringNernst equation: electrochemical cell potential and reaction quotient
Calculate a reversible cell potential from a supplied standard potential, temperature and dimensionless activity-based reaction quotient.
Read the guide →Engineering & ScientificNernst Equilibrium (Reversal) Potential & Electrochemical Driving Force
Compute ion reversal potential E_ion = (R*T / (z*F)) * LN([X]_out / [X]_in) in millivolts across temperature and valence, plus net transmembrane driving force V_m - E_ion.
Read the guide →Engineering & ScienceNernst-Planck Electrodiffusion Equation: Fickian Diffusion + Electric Migration Flux
Calculate total ionic molar flux J_i = -D_i * (dC/dx + ((z_i * F) / (R * T)) * C * (dPhi/dx)) in umol/(m^2*s) across PEM fuel cells, Li-ion electrolytes, and biological ion channels.
Read the guide →Econometrics & Discrete Choice ModelingNested Logit Inclusive Value (Logsum) and IIA Paradox Formula
Resolve Multinomial Logit’s Red-Bus/Blue-Bus IIA paradox using McFadden’s Nested Logit inclusive value IV = LN(SUM EXP(V_j / lambda)) and Random Utility consistency check 0 < lambda <= 1.
Read the guide →Lookup & ReferenceNested VLOOKUP & Chained XLOOKUP: Two-Hop Crosswalk Mapping Formula
Translate legacy ERP or vendor codes through an intermediate crosswalk bridge table into master pricing using IFNA(VLOOKUP(VLOOKUP(G2, A2:B5, 2, FALSE), D2:E5, 2, FALSE), "Unmapped Code") or chained XLOOKUP.
Read the guide →StatisticalNet Promoter Score (NPS) & CSAT Top-2-Box formulas with COUNTIF
Calculate NPS including passive respondents and a 1–5 top-two-box CSAT percentage from a validated eight-response sample.
Read the guide →Statistical & Clinical AnalysisNet Reclassification Improvement (NRI) & Integrated Discrimination Improvement (IDI)
Evaluate Michael Pencina’s biomarker incremental value metrics: additive Event + Non-Event NRI and probability-slope separation gain IDI = (IS_new - IS_old).
Read the guide →Dates and reportingNETWORKDAYS function: count working days excluding holidays
Count Monday-to-Friday working days between a start and end date inclusively, deducting weekday closures from a holiday range without double-counting weekend holidays.
Read the guide →Engineering & ScienceNeuber's Rule: Local Elastic-Plastic Notch Stress & Strain Concentration
Calculate the Neuber hyperbola product sigma * epsilon = (Kt * S)^2 / E (MPa) at geometric stress raisers and solve local notch-root total strain under elastic-perfectly-plastic yielding.
Read the guide →Engineering & ScienceNeutron Star Compactness (2GM/Rc^2), Gravitational Redshift & Buchdahl Limit
Calculate general-relativistic stellar compactness Xi = (2 * G * M) / (R * c^2), exact Schwarzschild surface gravitational redshift z_grav = ((1 - Xi)^-0.5) - 1, and verify Buchdahl's stability bound Xi < 8/9.
Read the guide →Engineering & ScienceNeutron Star Relativistic Compactness (Ξ), Surface Redshift & Buchdahl Limit
Calculate general-relativistic compactness Ξ = G*M / (R*c^2), NICER X-ray surface gravitational redshift z_surf = (1 - 2*Ξ)^(-1/2) - 1, and Hans Buchdahl’s Ξ < 4/9 collapse limit.
Read the guide →Healthcare & Clinical CalculationsNew Ballard Score (NBS) Neonatal Gestational Age Formula (20–44 Weeks)
Calculate clinical newborn gestational age in weeks GA = 24 + 0.4 * (Neuromuscular + Physical_Score) across Jeanne Ballard’s expanded -10 to +50 neonatal maturity scale.
Read the guide →Healthcare & ClinicalNew Orleans Criteria (NOC) Head CT Rule for GCS 15 Minor Head Trauma
Apply Michelle Haydel’s 7-item New Orleans Criteria (Headache, Vomiting, Age > 60, Drug/Alcohol Intoxication, Persistent Anterograde Amnesia, Visible Trauma Above Clavicles, Seizure) in GCS = 15 blunt head injury with LOC.
Read the guide →Statistical & Clinical AnalysisNewcombe Hybrid Wilson Score Confidence Interval for Two-Proportion Risk Difference
Construct boundary-respecting 95% confidence limits for independent risk difference RD = p_1 - p_2 using Robert Newcombe’s (1998) Method 10 square-and-add Wilson score intervals.
Read the guide →Time-Series Econometrics & ForecastingNewey-West Bartlett HAC Long-Run Variance and Standard Error Formula
Correct serially correlated regression or sample-mean standard errors using Newey and West’s (1987) Bartlett-kernel triangular weights w_j = 1 - j / (L + 1) that guarantee positive variance.
Read the guide →Network Science & Graph AnalyticsNewman-Girvan Network Modularity Q Partition Formula
Evaluate graph community clustering via Mark Newman and Michelle Girvan’s (2004) Modularity Q = SUM_c(e_cc - a_c^2) comparing intra-community edge share against the degree-preserving configuration null model.
Read the guide →Civil, Structural & Geotechnical EngineeringNewmark Seismic Sliding-Block Formula: Yield Acceleration k_y & Permanent Slope Displacement
Evaluate earthquake slope performance beyond pseudo-static failure using Nathan M. Newmark’s (1965) Critical Yield Acceleration k_y = (FS_static - 1) * SIN(beta) and Ambraseys-Menu permanent co-seismic displacement D_N (cm).
Read the guide →StatisticalNEWS2 Scale 1 spreadsheet exercise: scoring bands and single-parameter triggers
Practice IF and IFS with fictional NEWS2 Scale 1 observations, explicit input validation and the separate single-parameter three-point trigger.
Read the guide →StatisticalNewsvendor model formula: Critical Fractile & optimal perishable stock level
Calculate a single-period critical fractile and select an order quantity from five equally likely demand scenarios. Distinguish empirical demand quantiles from interpolated percentiles.
Read the guide →EngineeringNewton's Law of Cooling formula: transient temperature & time to cool
Calculate temperature and target time in a constant-ambient, constant-rate lumped cooling or warming model, with explicit reachability checks.
Read the guide →Date & TimeNext & Previous Working Day: Strict Step vs. Same-or-Next Business Day Roll
Calculate strictly next/previous working days and roll-forward/roll-backward settlement dates that preserve valid business days while skipping weekends and holidays via WORKDAY.
Read the guide →Date & TimeNext Biweekly Payday from Any Date formula (14-Day Anchor + CEILING.MATH)
Find the next date on or after a query date in a fixed 14-day schedule anchored to a known date.
Read the guide →Date & TimeNext business day N months in the future (EDATE + WORKDAY "-1, +1" trick)
Shift a date by whole months, then keep it if it is a working day or roll forward using a supplied holiday list and Saturday–Sunday weekends.
Read the guide →Date & TimeNext work anniversary date and completed years of service
Calculate completed employee tenure, exact upcoming anniversary date (leap-day safe), and 5-year service award milestones.
Read the guide →Healthcare & ClinicalNEXUS Cervical-Spine Trauma Clearance Criteria (5-Item NSAID Rule)
Evaluate Hoffman's 34,069-patient National Emergency X-Radiography Utilization Study (NEXUS) 5-item criteria to safely clear blunt trauma cervical-spine imaging with 99.6% sensitivity.
Read the guide →StatisticalNFL Quarterback Passer Rating formula (0 to 158.3 Official Scale)
Calculate NFL passer rating with four clamped components and compare it with adjusted yards per attempt (AY/A).
Read the guide →Fire Protection Engineering, NFPA 13 Hydraulic Calculations & Sprinkler DesignNFPA 13 Fire Sprinkler K-Factor Discharge & Pressure Formula
Calculate Minimum Head Flow Q_min (GPM), NFPA 13 Minimum End-Head Residual Pressure P_req (psi, enforcing >= 7.0 psi code floor), Actual Orifice Discharge Q = K*SQRT(P) (GPM), and Hydraulic Over-Discharge (%).
Read the guide →Underground Caverns, Drill-and-Blast Tunneling & NATM, NGI Barton Q-SystemNGI Barton Tunneling Q-System & Roof Support Formula
Calculate Logarithmic NGI Rock Mass Quality Q (0.001–1,000), Equivalent Excavation Dimension De (m), Maximum Permanent Unsupported Span (m), and Crown Support Pressure (kPa).
Read the guide →Precision Aerospace & Optical Tooling, Nickel Sulfamate Electroforming & Throwing PowerNickel Electroforming Wall Rate & Haring-Blum Throwing Power
Calculate Faraday Nickel Deposition Rate (um/h), Electroformed Mandrel Shell Thickness (um and mm), and Field-Modified Haring-Blum Throwing Power (%).
Read the guide →Panel Econometrics & Time SeriesNickell Dynamic Panel Fixed-Effects Bias Formula (Short-T Audit)
Quantify exact Nickell (1981) downward Fixed-Effects bias in dynamic AR(1) panels y_it = alpha_i + rho*y_{i,t-1} + u_it to decide when Arellano-Bond GMM is required.
Read the guide →Healthcare & ClinicalNIH Stroke Scale (NIHSS) Score (0–42) & Acute Stroke Severity Formula
Sum the 11 domain subscores of the National Institutes of Health Stroke Scale (NIHSS, 0 to 42 points) and stratify neurological deficit into Minor (1–4), Moderate (5–15), Moderate-to-Severe (16–20), and Severe (21–42) stroke.
Read the guide →OperationsNIOSH Lifting Equation: Recommended Weight Limit (RWL) & Lifting Index
Use supplied task multipliers to calculate a NIOSH recommended weight limit and numerical lifting index. Validate inputs and preserve precision without presenting a personal safe-lifting guarantee.
Read the guide →FinancialNOMINAL function: convert effective APY back to a stated annual rate (APR)
Find the stated nominal APR needed to hit a target effective annual yield under monthly or quarterly compounding using NOMINAL.
Read the guide →Math & StatisticalNon-Volatile Dynamic N-Period Sum & Average Without OFFSET (SUMIFS & AVERAGEIFS)
Replace slow volatile SUM(OFFSET(B2,0,0,N,1)) rolling windows with dependency-tracked SUMIFS(B2:B7, A2:A7, "<=" & E2) and AVERAGEIFS for instant multi-sheet recalculation.
Read the guide →Charts & Visual DataNormal Distribution Bell Curve Formula: Exact Gaussian PDF Ordinate & Sigma Grid
Generate smooth XY Scatter Bell Curve coordinates for any mean mu and standard deviation sigma using the universal closed-form Gaussian density formula (1 / (sigma * SQRT(2*PI()))) * EXP(-0.5 * z^2).
Read the guide →Statistical & Clinical AnalysisNormal Q-Q & Probability Plot Formula: Blom Plotting Position & Theoretical Z-Quantile
Build a Normal Q-Q (Quantile-Quantile) and Normal Probability Plot table from sorted sample data: compute Blom’s unbiased plotting position p_r = (r - 0.375) / (n + 0.25) and Tukey’s closed-form standard normal quantile z_r.
Read the guide →Engineering & ScienceNormal Zeeman Effect: Bohr Magneton Energy & Spectral Wavelength Splitting
Calculate Zeeman magnetic sublevel energy splitting delta_E = mu_B * B (in micro-electronvolts, mu_B = 57.8838 ueV/T) and Lorentz triplet wavelength shift delta_lambda = 4.66864e-5 * B * lambda_0^2 (in picometers).
Read the guide →StatisticalNormalize data between 0 and 1 (Min-Max scaling vs Z-score)
Rescale disparate KPIs onto a common 0–1 (or 0–100) scale with (x - MIN) / (MAX - MIN) or standardize into Z-scores.
Read the guide →Text & String FormulasNormalize Dirty Text Keys: Strip CHAR(160), Control Codes & Case (CLEAN & TRIM)
Sanitize web-scraped and ERP-exported lookup keys via LOWER(TRIM(CLEAN(SUBSTITUTE(A2, CHAR(160), " ")))) so invisible HTML non-breaking spaces and line breaks stop breaking XLOOKUP and VLOOKUP.
Read the guide →Text & CleaningNormalize Noisy Vendor & Bank-Feed Strings via Keyword Mapping (SEARCH & IFS)
Map messy corporate card and bank-feed descriptions containing terminal IDs, asterisks, and city suffixes to canonical vendor names using ordered ISNUMBER(SEARCH(...)) rules and SUMIF spend rollups.
Read the guide →Lookup & ReferenceNormalize storage units: binary KiB/MiB/GiB/TiB versus decimal GB
Use powers of 1024 for IEC binary units and powers of 1000 for decimal SI units; keep the two conventions distinct.
Read the guide →Electronics Packaging Reliability, IPC-9701 / JEDEC Norris-Landzberg BGA FatigueNorris-Landzberg BGA Solder Thermal Acceleration Formula
Calculate CTE Strain-Range Multiplier (dT_test/dT_field)^1.9, Creep Frequency-Arrhenius Factor, Total Acceleration Factor AF, and Equivalent Field Service Life (years).
Read the guide →