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

Horizontal, vertical and diagonal angle of view for a lens and sensor, and the width and height of scene covered at a distance.

Exposure value (EV) from aperture, shutter speed and ISO, the light level it suits, and equivalent aperture and shutter pairs.

Minimum handheld shutter speed (reciprocal rule) and the longest star-point exposure by the 500 rule and the NPF rule.

Loudness maths: gain to a LUFS target or platform, resulting true peak vs ceiling, or combining segment loudness.

Audio buffer size to latency in ms (one way and round trip) at a sample rate, or the buffer needed for a latency target.

Convert between linear amplitude and dBFS, and get the RMS level and crest factor of a sine, square, triangle or sawtooth.

Add, average or subtract sound levels in dB: total of several sources, N identical sources, or background-corrected level.

Audio file size from bitrate and duration, or the bitrate or duration it implies; PCM size from rate, depth and channels.

Dynamic range, levels and smallest step for a PCM bit depth, theoretical SNR, and the bit depth needed for a dB range.

Time-lapse planner: give any two of interval, shooting time and clip length to get the rest, frame count and storage.

Print size from image pixels at a DPI, or the pixels and megapixels needed for a print size; with viewing-distance advice.

ND filter maths: convert between ND factor, stops and optical density, and get the new shutter time with the filter on.

Depth of field from focal length, aperture, distance and sensor: near and far limits, total depth and hyperfocal distance.

Weekday of any date from year 1 to 9999 (Gregorian or Julian calendar) with day of year, quarter, ISO week and ISO week-date.

Convert a Gregorian date to the Islamic tabular civil calendar (or back); a calculated approximation, not moon sighting.

All new moons, first quarters, full moons and last quarters in a month (UTC) with times and a blue-moon flag.

Convert a Gregorian date to the Persian Solar Hijri calendar (or back) using the astronomical Nowruz rule, 1901-2100.

Is a year a leap year in the Gregorian, Julian, Hebrew, Islamic (tabular) or Persian calendar? Rule and nearby leap years.

Nyquist frequency for a sample rate, plus the alias frequency and samples per cycle of a tone, and the guard band above 20 kHz.