EV Step Is the HDR Record Nobody Saves
EV Step and Frames per Set are the HDR bracketing parameters. Together they describe the exposure bracket sequence: how many stops between each frame, and how many frames in the set. Three frames at 2 EV steps is a standard -2/0/+2 bracket. Five frames at 1 EV step is a tighter -2/-1/0/+1/+2 sequence that gives Lightroom or Photomatix more material for a natural-looking blend.
Most photographers who shoot HDR regularly have internalized the combinations that work for their typical subjects. The problem is "typically." When you're at a location with extreme dynamic range — a deep canyon with full sun overhead and shadows at the base, or an interior architectural shot with blown windows — the settings that work for your normal workflow may not be appropriate, and the record of what you tried and what produced usable results is what you want on the next visit.
The Promote Mid Exp field handles the Promote Control's middle-exposure anchor in time-blended sequences. Getting that anchor wrong on a timelapse-to-HDR hybrid sequence means the stacked frames won't align.
The GPS Field Closes the Location Loop
Map Location, GPS-pinned for each session. Not "Pacific Coast Highway north of Big Sur" — the actual coordinate where the tripod was positioned. The difference matters when you're returning to a location where five meters changes your foreground framing entirely, or when the exact shooting position puts you in a shadow window that only exists at a specific angle relative to a rock formation.
Paired with the Date field, the GPS location tells you what the sky looked like from that exact position at that time of year. After twenty sessions logged from different coastal locations across multiple seasons, the pattern of which spots produce dramatic light at which times of year becomes visible in the data.
The Event and Description fields are the human-readable context. The technical parameters are the reproducible record. Both are necessary — neither is sufficient without the other.