# Figure 6 digitization: Mach number and altitude

**Status: approximate graph readings.** The CSV is a plotted-trace digitization, not raw telemetry and not a reconstruction of unreported measurements. It contains only the Mach-number and `H/10 (km)` series; pressure and fuel-flow series were excluded.

## Source and method

Source: `sources/web/S-PROP-004-NASA-CIAM-MACH65.pdf`, physical page 4, Figure 6, “Flight trajectory information.” SHA-256: `8a9c844a03d20ee4b734e855cfe177f12c792f541b248293abb7096204837781`. The supplied 4x crop is `analyses/rendered-S-PROP-004-NASA-CIAM-MACH65-2026-09-29/figure-6-4x.png` (920 × 588 px). It was checked against a direct 4x rendering of the original PDF clip (page-coordinate rectangle x=315–545 pt, y=255–402 pt); the images match pixel-for-pixel. The original full page was also inspected to confirm the Figure 6 label, legend and surrounding text.

The plotted line geometry was read from the original PDF vector drawing and checked against the supplied crop. Coordinates below are in the supplied crop, with the image origin at upper-left:

- Horizontal calibration: `t=0 s` at `x=38.044 px`; `t=120 s` at `x=753.364 px` (5.96099 px/s).
- Vertical calibration for both left-axis series: ordinate `7` at `y=15.772 px`; ordinate `0` at `y=484.492 px` (66.896 px per ordinate unit; image y increases downward).
- Mach is the plotted left-axis ordinate. Altitude is labelled `H/10 (km)`, so altitude in km is ten times its plotted ordinate.

CSV rows are linearly interpolated at 5-second intervals, with an additional row at 56.5 s to compare against the report text. The last row (115.0 s) is endpoint-clamped to the plotted trace endpoint at about 114.99 s. Pixel-coordinate columns preserve each sampled trace location in the supplied crop.

Estimated reading precision is about ±0.05 Mach and ±0.5 km vertically, and ±0.3 s horizontally. The closely spaced altitude diamonds around 55–61 s make the individual marker centres less distinct; the altitude trace is nevertheless continuous. Its broad high plateau around 85–95 s does not support a precise graph-only peak time. These precision estimates describe reading the printed chart, not uncertainties reported by the experiment.

## Check against the report text

The page-4 narrative reports Mach 6.4 at booster burnout at 56.5 s, with maximum velocity 1,830 m/s. The digitized Mach trace gives about 6.39 at 56.5 s and peaks at about 6.40 near 56.5 s, consistent at the chart's reading precision.

The altitude text is internally inconsistent at that maximum-velocity point: one passage gives 21.4 km, while the later anomalies paragraph gives 21.6 km (rather than 24 km). The digitized altitude trace is about 21.5 km at 56.5 s. This note preserves both source-text values and does not adjudicate them.

For maximum altitude, the text reports 27 km at 90 s. The plotted trace reads about 27.3 km at 90 s and has a broad maximum of roughly 27.4 km around 85–95 s. This is compatible with the text's whole-kilometre reporting precision; the graph alone cannot select an exact peak time within the plateau.

## Files

- `candidate-points.csv` — 25 approximate samples (0–115 s every 5 s, plus 56.5 s).
- `digitize_traces.py` — reproducible extraction/interpolation and source-hash check.