How to mark a scroll's centre

A rolled scroll winds around an imaginary line from one end to the other, the umbilicus. Your job is to mark where that line passes through the scan's slices. On the carbonised Herculaneum rolls nothing of the rod is left, so the centre is simply the middle of the innermost turn. Our unrolling program counts the turns outward from your centre, so it must be close: aim for about 50 voxels (half a millimetre). Greek is not needed; this is about shapes.

1. Practise first

Open the practice scroll from the list. Its centre was published by the organisers. Place a point on each of the five slices shown, then press Show the answer rings. The pass mark is 4 of 5 inside the outer ring (100 voxels). The organisers' points were also placed by hand, so a near miss on a crushed slice can be theirs as much as yours.

2. Move around

• Use Chrome on a computer with a mouse. The scan arrives in pieces; each new area takes up to a minute to sharpen.
• Mouse wheel (or the , and . keys) moves one slice; Shift + wheel moves 10.
• Control + wheel zooms; drag moves the picture; right-click centres the view on a spot.
• To jump to a slice, use the Go to slice button in the side panel, or click the z number at the top left of the viewer, type it and press Enter.
• Shift + drag tilts the slice. If the picture looks smeared or the slice number changes by itself, press z to straighten it, then go back to your slice.
• Before clicking anything, roll through the whole scroll once. The core is far easier to recognise moving than still.

3. Find the core and click it

• Look for the place the layers wrap around, like wood grain around a knot. In a well-kept slice it is an open eye: a small dark or speckled hollow ringed by the innermost turns. In a squashed scroll it is a thin dark slit whose two sides run parallel and make a hairpin turn at each end.
• Zoom in until the core fills about a third of the screen. Roll 50 slices up and down: the true core keeps its shape and drifts only a little.
• Don't aim at the middle of the scroll's outline. The core is often several millimetres to over a centimetre away from it.
• Control + click the middle of the hollow. For a slit, click the dark line inside it, halfway between its two hairpin ends, the same way on every slice. Never click on a papyrus layer.
• One point on every slice ending in 00. If the core moves more than about 100 voxels between two of your points, add one halfway between them.
• Not sure? Click your best guess, then type ? (and a few words if they help) in the point's Description box at the lower right.
• Wrong spot? Click the point in the list on the right of the viewer, then the bin icon. Or hold Control and Alt (Option on a Mac) and right-click the dot.

4. Hard cases

• A gap is not a core. Cracks look like slits, but their walls don't turn around them. At a real core the innermost layer makes a hairpin at each end.
• The wrong branch. A fold outside the core can look like a turning point. Trace the innermost two or three layers from your point: each should go all the way round, or hairpin back.
• Bright debris often fills the hollow and helps you find it, but bright grains elsewhere are not a core.
• Two cores. A crack can make a scroll seem to have two centres for a stretch. Stay on the one that continues the line from the slices below, and add a ? note.
• Nothing visible. Don't invent a point. Skip the slice; a gap is better than a wrong point.

5. Saving and finishing

Your points save themselves every few seconds; the side panel says when. If a scroll is open in two tabs, only one can save, so keep one tab per scroll. The side panel lists anything worth a second look: two points on one slice, gaps of more than 150 slices, and jumps of more than 100 voxels per 100 slices. When a scroll is done, press I've finished this scroll. Work in sittings of an hour or two; tired eyes make worse calls.

Please keep pictures and points from this site private.