A count that excludes both the first day and the last — so 'three clear days' is longer than three days.
Clear days is a counting rule, not a kind of day. Where a period is expressed in clear days, both the day the period starts and the day it ends are excluded from the count.
Three clear days' notice before a Friday meeting therefore means notice by Monday, not Tuesday: Tuesday, Wednesday and Thursday are the three clear days, and neither the day of service nor the day of the meeting counts.
It appears constantly in court rules, company law and constitutional documents, and it is the sort of provision that is read quickly and applied wrongly. The failure is always in the same direction — one day short — because the natural reading includes an endpoint the rule excludes.
Working day is what you count. Clear days is a rule about which ends of the count to include, and the two combine — a period can be in clear working days.
See also working day · business day · deadline
We hold this as not held — a rule of construction, not a calendar fact. See what we hold.