The shot that built this: golden hour, a borrowed medium-format camera loaded with slide film, and the handheld meter sitting uselessly at home on the bookshelf. The phone in my pocket contained a photon-counting sensor considerably better than anything Weston ever sold — with no way to just ask it how much light there was. Guessed the exposure, blew the roll a stop and a half over, learned the lesson. A camera's auto-exposure is a light meter answering a different question; the work here was making it answer the photographer's one, and printing the error bars where you can see them.
— the bookshelf meter has since been forgiven, and mostly retired
My phone has three cameras — which one is metering?
The default rear camera opens first, usually the main wide lens. Where the browser can list the others, a camera dial appears and you can switch; each camera remembers its own aperture once you set it (the spec sheet lists them; f/1.8 is the common answer for the main lens). If no dial shows, your browser is keeping the list to itself — the default eye is still a calibrated one.
Can I meter for flash with this?
No — flash metering needs to catch a burst measured in thousandths of a second, which is a genuinely different instrument. Ambient light only, which covers available-light film work, landscapes, and the eternal "what ISO do I need indoors" question.
Does the reading work through a window, for the scene outside?
Yes, minus the glass's toll — clean single glazing eats maybe a third of a stop, tinted or double glazing more. Meter outside when the shot is outside, if you can.
Why does the EV jump when something moves through the frame?
Because the scene genuinely changed, and centre-weighted metering felt it. For a stable reading of the light itself, spot-meter something fixed and mid-toned — pavement, grass, a wall — and use hold while you transfer settings.
What's the palm trick the FAQ mentioned?
Skin is about one stop brighter than a mid-tone. Spot-meter your palm in the same light as the subject, then open up one stop from what the calculator says — a grey card you never forget to pack.
What is reciprocity failure, and do I care?
Past about a second, film stops keeping its side of the bargain: double the time no longer means double the exposure, so long shots come out thin unless you give extra. Pick your stock in the calculator's film dial and the correction is folded in automatically — or work it by hand on the reciprocity page. Digital sensors don't care; film very much does.