The small slate boards used by Wrenhaven's pilots were about the size of a bread plate, with rounded corners and a hole for a cord. Their wooden frames were darkened by hands and weather. Most had a pencil tied to them, although a practical owner also kept a spare in a coat pocket.
A board might carry a berth number, the expected draught of an arriving vessel or a message about the condition of the lower channel. These were temporary facts, useful for an hour or an afternoon. Paper remained necessary for the account books; the slate occupied the shorter interval between learning something and acting on it.
Pilot Jonah Trell distinguished his own board by cutting three shallow notches in its frame. On crowded mornings, several boards could lie together on the office table. The notches let him identify his without turning it over and rubbing out a message that another man had written on the reverse.
An attempt to standardise the boards produced a longer argument than the purchase itself required. A larger size would hold more information, but would not fit the usual pockets. A white painted surface was brighter, but its marks were harder to remove completely. The existing slate survived both proposals.
The worn frames explain something about this modest system. Accuracy did not depend on a single handsome document. It depended on readable marks, timely corrections and the habit of asking whether a number was still current. The boards were useful because everyone understood that they would shortly be wiped clean.