A compact sequence of point-like and streak-like images appears to be an exposure comparison. The spatial arrangement is useful, but a celestial coordinate model is not justified.
The margin appears to record Polaris calibration, 24 September 1917, 25 exposures, a 3-second setting and a 17½-inch aperture. The regular dots are repeated records whose instrumental roles need confirmation. They cannot be counted as independent field stars or used to derive a glass warp without a separate sky reference.
The main photographic signal is organized into comparison columns rather than a rich, independent star field. Repeated target images can encode controlled exposures without supplying astrometric geometry.
The margin appears to include “Calibration Polaris”, “1917 Sept. 24”, “25 exp.”, several durations in seconds, “17½” aperture” and “Seed 30”. These visual readings give a concrete route to an exposure-response study, but target identity, units and entry-to-image pairing still require verification.
The revised layer uses local contrast in both polarities, expanded inspected writing regions and contextual recovery of short fragments and round digits. Known photographic targets and sampled spectral apertures are protected. It is not OCR and does not reconstruct hidden sky or invent pen strokes.
The selection covers 4.30% of this scan (904,373 pixels). Faint marks, scratches and contacts between ink and photographic images remain ambiguous. The cyan overlay shows the wider exclusion footprint used by the photographic remainder; the stroke mask is supplied separately.
The writing PNG is a white, contrast-rendered stencil of bright and dark observed marks. The observed-pixel PNG preserves their stretched scan appearance. Both use original scan coordinates. The photographic remainder displays excluded pixels as black holes. It is neither a clean-sky reconstruction nor a new photometric product. Keep the mask alongside any measurements. Native original-intensity TIFF/FITS products, where generated, remain in the analysis workspace and are not duplicated in this handoff.
This revision recovers short letter fragments, round digits and inspected dark marks, with broader writing regions. The stroke selection grows from 648,512 to 904,373 pixels (1.39×). The photographic remainder uses a separate 3-pixel exclusion margin, covering 7.98% of the scan.
The wider selection deliberately favors removing writing. Nearby stars, scratches and ambiguous fragments can also be excluded. Explicit photographic protection regions retain known target images and sampled spectra; this does not establish perfect separation elsewhere.
No direct star-field solution is reported. The current classification is an exposure-comparison specimen based on visual structure, not a verified historical plate type.
The margin appears to record Polaris calibration, 24 September 1917, 25 exposures, a 3-second setting and a 17½-inch aperture. The regular dots are repeated records whose instrumental roles need confirmation. They cannot be counted as independent field stars or used to derive a glass warp without a separate sky reference.
Across these scans, repeated photographic images need not imply the same mechanism. Shutter timing, guiding offsets, objective optics and different pointings can leave related patterns. Establish consistent component membership before fitting a smooth warp. No result here isolates glass deformation from telescope optics, emulsion, scanner geometry and centroid bias.
The natural next measurements are profile width, integrated signal and saturation in native scan pixels. Converting them to exposure response needs a verified schedule and a scanner/emulsion model.
The candidate writing layer and binary mask are included. There is no physical distortion correction or resampled scan, and no catalog image is fetched without a justified sky position.
Select a numbered pin or a note. Locations are editorial review pointers, not measured confidence contours; plate-wide limitations also apply.
Target identity and which exposure parameter varies are unknown.
Labels near photographic signal can be incomplete or mixed in the mask; their units are not established.
The historical record may explain the sequence and its relation to R3663.
Transcribe both R3662 and R3663, identify matched entries from the notes, and measure profiles using identical native-pixel apertures and saturation rules.
The specimen supports an exposure-comparison investigation. It does not yet support a sky identification or an empirical glass map.
All scientific numbers are snapshots of the saved analysis products. The original 16-bit scans remain the measurement source. JPEG derivatives, contrast stretching and masked previews are inspection tools; do not derive photographic density or absolute response from their appearance.
