RC filter cutoff frequency, time constant and charge times to 63%, 90% and 99% from resistance and capacitance.

Decode 3 to 6 resistor color bands to ohms, tolerance and temperature coefficient, or encode a value into 4 or 5 bands.

Area, perimeter, surface area and volume of circles, polygons, sectors, spheres, cylinders, cones, boxes, tori and more.

Solve linear equations Ax = b (up to 6 unknowns): unique, none or infinite solutions, with rank and determinant.

555 timer calculator: astable frequency, period and duty cycle from R1, R2 and C, or monostable pulse width from R and C.

Solve ax^3 + bx^2 + cx + d = 0: all three roots (real and complex) by Cardano and the trigonometric method.

Complex number arithmetic, modulus and argument, integer powers, square root and n-th roots, in rectangular and polar form.

Health of a Ruby gem on RubyGems: latest release age, downloads, license, version counts, owners and links.

Health of a Docker Hub image: official or not, pulls, stars, last push age, recent tags and supported architectures.

Health of a .NET NuGet package: latest release age, downloads, verified owner, deprecation and known-vulnerability flags.

Crop factor of a sensor, with the full-frame equivalent focal length, aperture and ISO for a lens, or a custom sensor size.

Health of a PHP Composer package on Packagist: latest stable release age, downloads, license, abandonment and GitHub signals.

Classify an SPDX license expression such as MIT OR Apache-2.0: permissive, copyleft or restricted, with the effective result.

Health of a Go module via the official proxy: latest tagged version, release age, repository origin and pseudo-version warning.

Health of a Rust crate on crates.io: latest release age, downloads, license, yanked versions, owners and repository.

Homebrew formula status: version, license, deprecation or disablement, install counts over 30, 90 and 365 days.

Vector operations: dot and cross product, magnitudes, angle between vectors, projection, unit vectors and distance.

Flash guide-number maths: range for an aperture and ISO, or the aperture needed for a distance, in metres and feet.

Hold exposure constant: change one setting (aperture, shutter or ISO) and get the other two compensations, in stops.

Convert a frequency ratio (3:2) to cents and semitones or back, name just and Pythagorean intervals and commas, apply to Hz.