Reciprocity Crossover Alert tied to ephemeris
Predicts the shutter at every twilight event and warms the chip when reciprocity bites.
Where to find it
Tools tab Sun & Moon, second line under each event row
Summary
A second line under each Sun & Moon event predicts the shutter speed for the loaded film stock at the user's selected aperture, derived from the sun's altitude at that event. The shutter snaps to the same ring the live meter uses (current StopIncrement, gear-derived or custom min/max range), routes long exposures into Bulb when the body supports it, and switches to the tertiary accent color with raw -> corrected stops when reciprocity bites.
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How it works
Knowing what time golden hour starts is half the planning. The other half is knowing what shutter you are actually going to need at that time on the film you have loaded. This feature does that math for every event in the Sun & Moon list, and tells you when reciprocity correction is going to make the exposure noticeably longer than the meter says.
Where the chip appears
Open Sun & Moon and look just below the time-and-duration line on each event row. With a film stock loaded other than 'No film selected', a small text chip shows the stock, the aperture, and the predicted shutter at that event. Rows past the polar-day or polar-night boundary still show no chip.
How the prediction works
The sun's altitude at each event is known by definition: civil twilight is the sun at minus 6 degrees, golden hour is the sun at plus 6 degrees, sunrise is the sun at the horizon, and so on. Solar noon's altitude is computed from your latitude and the date. Each altitude maps to a standard ambient EV at ISO 100 (Adams' Negative, Sekonic L-758 reference, ISO 2720 sunny-16 derivations). The exposure solver then finds the shutter at your aperture and the film's box ISO.
Shutter values match your camera
The chip never shows a shutter your camera can't dial. The predicted time is snapped to the same ring you scroll on the main screen (1/250, 1/125, 1/60, etc., in your active full / half / third stop increment) and stays inside the gear-derived or custom range you set under Equipment. When the predicted time is slower than the slowest available shutter and the body has Bulb, the chip shows 'B 4m 32s' the same way the live meter does. Without Bulb, the chip shows '> max' to flag that the camera can't reach the predicted exposure.
When the chip turns warm
If the raw shutter at that event would cross 1 second and the loaded film has a reciprocity exponent above 1.0, the chip switches to the tertiary accent color and shows two times: the metered shutter and the corrected shutter, plus the number of stops reciprocity adds. For example: 'Tri-X 400 @ f/2.8 30s -> B 1m 32s +1.7 stops'. Films with no reciprocity correction (Acros II, Provia 100F) stay neutral and just show the shutter.
Limits and caveats
The EV table assumes clear sky at sea level. Heavy overcast, dense forest, snow on the ground, or shooting from 3000 m altitude can shift the prediction by up to two stops. The chip is a planning tool: at shoot time, take a real meter reading. Box ISO is used for the prediction even if you are pushing or pulling at development time.