Session high and low

The session high and low are the highest and lowest prices reached during one of the named trading sessions, carried forward afterwards as reference levels on the chart. They are read the same way any prior extreme is read — as a price the market has already been to — and they are popular partly because they are unambiguous to compute once the session's start and end are settled. Settling those is the whole difficulty. The named sessions describe when particular financial centres are working, not anything the market itself switches on, and they are marked against a clock that shifts through the year as different regions change their local time. A platform showing times in its server's zone will therefore draw session boundaries somewhere that need not match the reader's own. The levels are also only final once the session has closed; before that they can still be exceeded, and a chart drawn mid-session is showing a running figure rather than a settled one.