A list of things to be done or verified, marked off as each is met. It defends against forgetting rather than against ignorance.

An ordered enumeration of things. First the strip of cloth at an edge - the border became the record written along it.

A short record set down so it is not lost. Also a single sounded pitch.

Small notes placed where they will be seen. They hold a thought outside a head so it need not be carried.

The erasable shared surface — thinking made visible, together, and wiped clean without loss of what it taught.