Learn one useful thing today.
DAYS function: count elapsed calendar days between two dates
Calculate exact calendar days between an issue date and settlement date, remember that end_date comes first, and interpret negative results for early settlements.
Read the guide →Date & TimeDays Until Next Anniversary or Renewal Ignoring Year (DATE Rollover)
Calculate exact calendar days remaining from a reference date until the next annual birthday, contract renewal, or calibration month/day—rolling cleanly into YEAR(ref) + 1 when this year’s date has passed.
Read the guide →Dates & TimeDays Until Next Annual Birthday or Contract Renewal (Ignoring Original Year)
Calculate exact calendar days from a reference date until the next annual birthday, SaaS renewal, or calibration date—wrapping cleanly across December 31 into next calendar year.
Read the guide →Date & TimeDays until next birthday: rollover-safe annual countdown
Project a birthdate into the current calendar year with EDATE, advance 12 months if it already passed, and subtract AsOfDate.
Read the guide →Server Power Architecture & Energy Storage SizingDC-Link Hold-Up Capacitor Line-Dropout Sizing Formula
Calculate Server PSU Dropout Energy Demand (Joules), Usable Capacitor Discharge Fraction 1 - (V_min / V_nom)^2, Required Bulk Hold-Up Capacitance C_uF = (2000 * P_out * t_ms) / (eta * (V_nom^2 - V_min^2)), and Nominal Stored Joules.
Read the guide →FinancialDCF valuation formula: NPV of cash flows plus Gordon Growth Terminal Value
Calculate Enterprise Value by combining NPV of explicit forecast Free Cash Flows with discounted perpetuity Terminal Value.
Read the guide →Equity Capital Markets, De-SPAC Mergers & Corporate DilutionDe-SPAC Redemption Dilution & Net Cash Per Share Formula
Calculate Post-Redemption De-SPAC Net Cash Delivered to Target Balance Sheet, Total Public + PIPE + Sponsor Promote Shares Issued, Effective Net Cash Per Share vs $10.00 Nominal Merger Price, and Total Dilution Cost % of Net Cash.
Read the guide →Semiconductor Fabrication, CMOS Front-End & Furnace OxidationDeal-Grove Silicon Thermal Oxidation Thickness & Tau Formula
Calculate Pre-Existing Oxide Time Shift tau (hr), Final SiO2 Gate/Field Oxide Thickness x_o (nm), Net Oxide Grown (nm), and Consumed Silicon Substrate Depth (0.46 * dx nm).
Read the guide →Engineering & ScienceDean Number (De) Curved-Pipe Vortices & Ito Critical Reynolds Formula
Calculate W. R. Dean’s secondary-vortex number De = Re * SQRT(D / (2 * R_c)) in helical coils and pipe bends alongside Hidesato Ito’s curved-pipe laminar-to-turbulent stabilization threshold Re_crit = 2100 * (1 + 12 * SQRT(D / (2 * R_c))).
Read the guide →Macroeconomics & Sovereign Fiscal AnalysisDebt Sustainability (r - g) & Stabilizing Primary Balance
Project public debt-to-GDP d_t = ((1 + r)/(1 + g)) * d_{t-1} - pb_t and calculate the exact debt-stabilizing primary balance pb* = ((r - g)/(1 + g)) * d_{t-1}.
Read the guide →Sovereign Debt & Public MacroeconomicsDebt-Stabilizing Primary Balance & (r - g) Formula
Project public debt-to-GDP dynamics d_t = ((1 + r)/(1 + g))*d_{t-1} - pb_t and calculate Olivier Blanchard’s (2019) debt-stabilizing primary balance pb* = ((r - g)/(1 + g))*d_{t-1}.
Read the guide →Engineering & ScienceDebye T³ Law: Low-Temperature Phonon Molar Heat Capacity Formula
Calculate cryogenic lattice molar heat capacity C_V = (12/5) * π^4 * R * (T / Θ_D)^3 (J/(mol·K)) from crystal Debye temperature Θ_D vs. the classical 3R Dulong-Petit ceiling.
Read the guide →Engineering & ScienceDebye-Scherrer XRD Crystallite Size & Peak FWHM Broadening Formula
Calculate mean nanocrystalline domain size D = (K * lambda) / (RADIANS(SQRT(FWHM_obs^2 - FWHM_inst^2)) * COS(RADIANS(2*theta / 2))) in nanometers from powder X-ray diffraction peaks.
Read the guide →Clinical Medicine & PhysiologyDECAF Score Calculator: Acute Exacerbation of COPD In-Hospital Mortality Triage
Calculate John Steer et al.’s (2012, Thorax) DECAF Score (0–6 points) for patients hospitalized with Acute Exacerbation of COPD (AECOPD) to identify Low-Risk Hospital-at-Home candidates (0–1) vs High-Risk inpatient mortality (>= 3).
Read the guide →EngineeringDecibel (dB) Power Gain, Voltage Gain & Logarithmic Sound Addition
Calculate 10*LOG10(P2/P1) power gain vs 20*LOG10(V2/V1) amplitude gain and add independent decibel sound levels accurately via 10*LOG10(10^(L1/10) + 10^(L2/10)).
Read the guide →Statistical & Clinical AnalysisDeeks’ Funnel Plot Asymmetry Test: Diagnostic Meta-Analysis Effective Sample Size (ESS)
Avoid spurious Egger false positives in Diagnostic Test Accuracy (DTA) meta-analyses by computing Deeks’ Effective Sample Size ESS = (4*n_1*n_2)/(n_1 + n_2) and regressing ln(DOR) on 1/SQRT(ESS).
Read the guide →Sheet-Metal Deep Drawing, Battery Cans, Beverage Shells & Stamping Forming LimitsDeep-Drawing Cup Blank Diameter, Draw Ratio & Force Formula
Calculate Surface-Area-Conserved Circular Blank Diameter D_b (mm), Actual Draw Ratio beta = D_b / d_p, Siebel Punch Drawing Force (kN), and First-Draw LDR Tear Check.
Read the guide →Sheet-Metal Stamping & Press-Shop Die Cushions, Siebel Blank-Holder Pressure & LDR GateDeep-Drawing LDR & Siebel Blank-Holder Cushion Formula
Calculate First-Draw Ratio Beta (D0 / dp), Siebel Anti-Wrinkling Blank-Holder Pressure pbh (MPa), Required Nitrogen/Pneumatic Die-Cushion Force (kN), and LDR Single-Stage Gate.
Read the guide →Geotechnical Core Logging & Rock Mass Characterization, ASTM D6032 Deere RQD & Priest-HudsonDeere Rock Quality Designation (RQD) & Joint Frequency
Calculate Total Core Recovery TCR (%), ASTM D6032 Measured Deere RQD (%), Priest & Hudson Theoretical RQD* (%) from Scanline Frequency lambda, and Palmstrom Volumetric Joint Count Jv.
Read the guide →Dynamic ArraysDefine a Dynamic Range Sized by a Cell Value (TAKE & OFFSET)
Choose the first N rows of a fixed revenue range with TAKE or OFFSET, enforcing an integer count and complete numeric data before computing totals and averages.
Read the guide →FinancialDegree of Operating (DOL), Financial (DFL), and Combined Leverage (DCL) formulas
Measure how fixed operating costs and debt interest magnify revenue swings into EBIT and EPS volatility via DOL, DFL, and DCL = DOL * DFL.
Read the guide →MathDEGREES function: convert radian outputs from ATAN, ASIN, and ACOS into degrees
Turn radian arc values and inverse-trigonometric results into readable degree angles using DEGREES.
Read the guide →Mixed-Signal IC Design, Delta-Sigma Data Converters & DSP DecimationDelta-Sigma ADC Oversampling Ratio (OSR) & ENOB Gain Formula
Calculate Mixed-Signal ADC Oversampling Ratio OSR = f_s / (2*BW), Plain Nyquist Oversampling Extra Bits (+0.5 bit/octave), First-Order Delta-Sigma Noise-Shaping SNR Improvement (dB), and Total Effective Resolution Bits (+1.5 bits/octave).
Read the guide →Statistical & PsychometricsDeming & Orthogonal Regression Slope Formula (Errors-in-Variables CLSI EP09)
Eliminate regression dilution bias when both X and Y contain measurement noise using W. Edwards Deming’s exact variance-ratio slope b_1 = (s_yy - δ*s_xx + SQRT((s_yy - δ*s_xx)^2 + 4*δ*s_xy^2)) / (2*s_xy).
Read the guide →Computer Architecture & Thermal Chip DesignDennard Scaling Breakdown & Dark Silicon Formula
Calculate Full-Chip Unthrottled Dynamic Power alpha * C_nF * V_DD^2 * f_GHz, Total Unthrottled Die Power, Thermal Design Power (TDP) Active Lit-Silicon Fraction, and Power-Gated Dark Silicon Share.
Read the guide →Data Validation & HygieneDependent Dropdown Conditional List Formula (FILTER & Parent-Child Audit)
Generate a dynamic cascading list of valid child options for a selected parent category using FILTER and UNIQUE, and audit existing rows to catch mismatched parent-child pairs.
Read the guide →FinancialDepreciation methods compared: Straight-Line (SLN), SYD, and Double-Declining
Calculate Year-1..N asset depreciation under Straight-Line, Sum-of-Years'-Digits, and salvage-capped Double-Declining Balance.
Read the guide →Statistical & PsychometricsDerSimonian-Laird Random-Effects Variance (τ²) & Higgins I² Meta-Analysis
Calculate between-study random-effects heterogeneity variance τ^2 = MAX(0, (Q - (k - 1)) / (Σw - Σw^2 / Σw)) and Higgins I^2 (%) from Cochran’s Q and fixed-effect weights.
Read the guide →Collaboration & Sharing WorkflowsDesign a 20x10 Public View Summary Block vs Named Workbook Invitations
Structure top-left KPI summary blocks for anonymous 20-row by 10-column public view pages, cross-foot totals against detail rows, and separate public links from named role invitations.
Read the guide →Dates & TimeDetect Schedule & Room Double-Booking Conflicts (COUNTIFS Overlap)
Flag overlapping conference-room, vehicle, or shift reservations on the same resource using De Morgan's interval overlap rule COUNTIFS(Resource, A2, Start, "<" & C2, End, ">" & B2) - 1 > 0.
Read the guide →Clinical Medicine & PhysiologyDeurenberg Body Fat % from BMI Formula: Adult (>= 16 yr) & Child Age-Sex Equations
Estimate underwater-weighing Percent Body Fat (%BF) from BMI, Age, and Sex using Paul Deurenberg et al.’s (1991, Br. J. Nutr.) adult equation (1.20*BMI + 0.23*Age - 10.8*Male - 5.4) and pediatric equation (1.51*BMI - 0.70*Age - 3.6*Male + 1.4).
Read the guide →Air Pollution Control, Power-Plant Flue Gas & Electrostatic SeparationDeutsch-Anderson Electrostatic Precipitator (ESP) SCA Formula
Calculate Electrostatic Precipitator Specific Collection Area (s/m), Deutsch-Anderson Collection Efficiency (%), Outlet Stack Dust Concentration (mg/m³), and Plate Area Required for 99.9% Removal (m²).
Read the guide →Commercial Real Estate DevelopmentDevelopment Yield-on-Cost & Interest Reserve Formula
Solve Construction Loan Interest Reserve IR = (k * C_hs) / (1 - k) without circular spreadsheet references, Total Project Cost, Stabilized Yield on Cost (YoC), and Development Spread.
Read the guide →StatisticalDevine weight, an adjusted-weight example and predicted body weight
Compare distinct weight equations with explicit units and assumptions; demonstrate why similarly named estimates should not be substituted blindly.
Read the guide →EngineeringDew Point temperature formula (Magnus equation) & condensation risk check
Estimate dew point over liquid water from air temperature and relative humidity using a Magnus approximation.
Read the guide →LogicalDiagnose & Prevent #NUM!, #REF!, and #NAME? Formula Errors
Prevent #NUM! domain errors (negative SQRT/LOG or k > COUNT in LARGE/SMALL), #REF! out-of-bounds INDEX lookups, and #NAME? unquoted strings or function typos using proactive boundary guards.
Read the guide →Lookup & ReferenceDiagnose XLOOKUP #N/A: Text Numbers and Unwanted Spaces
Test a deliberate text-first, numeric-fallback lookup policy, distinguish true text from numeric cell entry, and avoid silently changing meaningful identifiers.
Read the guide →StatisticalDiagnostic Sensitivity, Specificity, Youden's J & Likelihood Ratios (LR+/LR-)
Calculate sensitivity, specificity, Youden’s J and likelihood ratios from a fictional binary-classification table, with explicit checks for undefined ratios.
Read the guide →Banking & Financial IntermediationDiamond Delegated Monitoring & Diversification Formula
Calculate Douglas Diamond’s (1984) delegated-monitoring cost advantage of a diversified bank over duplicated direct saver monitoring (m*K) and unmonitored debt.
Read the guide →Banking, Liquidity & Financial StabilityDiamond-Dybvig Bank-Run Threshold & Liquidity Formula
Solve the Diamond-Dybvig optimal risk-sharing deposit contract (c_1*, c_2*), liquid reserve share t * c_1*, and critical withdrawal fraction f_crit* triggering a rational bank run.
Read the guide →Public Economics & Income DistributionDiamond-Saez Optimal Top Marginal Rate & Pareto Formula
Estimate the Pareto income tail index a = z_bar / (z_bar - z*) and compute the Diamond-Saez optimal top bracket rate tau* = (1 - g) / (1 - g + a * e).
Read the guide →High-Pressure Die Casting (HPDC), NADCA P-Q^2 Gating & Cold-Chamber Shot ControlDie-Casting Gate Area, Cavity Fill Time & Plunger Speed Formula
Calculate Cavity+Overflow Melt Volume (cm³), Volumetric Injection Flow Rate Q (cm³/s), Required Ingate Cross-Sectional Area A_g (mm²), and Cold-Chamber Fast-Shot Plunger Speed (m/s).
Read the guide →Forecasting & Demand PlanningDiebold-Mariano and HLN Forecast Accuracy Test Formula
Test whether two competing models have equal out-of-sample forecast accuracy using Diebold-Mariano loss differentials d_t and Harvey-Leybourne-Newbold’s finite-sample correction.
Read the guide →Econometrics & Causal InferenceDifference-in-Differences (DiD) Causal Estimator and Pre-Trend Check
Calculate the canonical 2x2 Difference-in-Differences ATT = (Y_T,post - Y_T,pre) - (Y_C,post - Y_C,pre), counterfactual level, and pre-intervention placebo trend test.
Read the guide →Machine Design, Hoist & Drawworks Differential Band Brakes & Self-LockingDifferential Band Brake Force & Self-Locking Check Formula
Calculate Euler Band Tension Ratio exp(mu*theta), Tight & Slack Band Tensions T1 & T2 (N), Differential Lever Actuating Force F (N), and Self-Locking Grab Detection.
Read the guide →Chemical, Process & Catalysis EngineeringDifferential Batch Distillation Formula: Remaining Still Pot Moles W & Composite Purity x_D
Calculate remaining kettle liquid W (mol), boiled-off overhead distillate D = F - W, and pooled composite distillate purity x_D,avg in single-stage constant-alpha batch distillation via Lord Rayleigh’s (1902) integrated VLE material balance.
Read the guide →EngineeringDilution (C1*V1 = C2*V2) and two-stock blending (Pearson Square) formulas
Calculate a stock volume from concentration balance and illustrate two-stock blending under an additive-volume assumption.
Read the guide →MathDimensional Weight (DIM Weight) vs. Actual Weight billable shipping formula
Compare dimensional and scale weight using a supplied divisor and an explicit whole-pound rounding assumption.
Read the guide →Petroleum & Geothermal Wellbore Surveying, MWD Directional Drilling & Torque/DragDirectional Drilling Dogleg Severity & Minimum Curvature Formula
Calculate 3D Spherical Dogleg Angle beta (deg), Normalized Dogleg Severity DLS (deg/30 m), Minimum-Curvature Ratio Factor RF, and True Vertical Depth Step Delta_TVD (m).
Read the guide →FinancialDiscount irregular dated cash flows on a 365-day basis
Discount cash flows arriving on exact irregular calendar dates using SUM(CashFlows / ((1 + Rate) ^ ((Dates - StartDate) / 365))).
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