Which Extended Hours Prints Belong on the Chart
Charts are supposed to agree with each other. Two traders looking at the same ticker will disagree about where the previous day high sits, and neither of them is wrong, because one platform is including extended hours prints and the other is not. This is where orb trading stocks bizstone sets the convention explicitly rather than accepting a default, since trading the opening range on equities means drawing levels, and a level derived from a different set of prints is a different level.
The Setting Nobody Remembers Changing
Every charting package has a toggle for extended hours data, and the default varies by platform, by chart type and sometimes by symbol. Turning it on adds every print from four in the morning through eight at night. Turning it off restricts the chart to the session between the opening bell and the closing bell. The toggle is usually set once during installation and then forgotten, which is how two screens on the same desk end up disagreeing.
What It Changes
The previous day high and previous day low move. The overnight high and overnight low either exist or do not. Any moving average or vwap computed from the visible bars shifts. Gap measurements change, because the reference close is different. A level written down last week from a chart with one setting will not match this week's chart with the other, and the mismatch is silent.
Thin Prints Are Real but Not Representative
A five hundred share trade at six in the morning is a genuine transaction and a poor description of value. Included on the chart it can set a high that no amount of regular hours activity ever revisits, and any rule keyed to that high is keyed to one small order. Excluded, the same information is still available on the tape and in the premarket range, just not as a candlestick claiming equal weight with the rest of the session.
A Workable Convention
The one used by most people who trade single names is to compute levels from regular trading hours only, and to keep the extended session visible on a separate panel or as marked lines. Structure comes from the continuous session where participation is real. Context comes from the overnight session, clearly labelled as such. Neither is discarded and neither is allowed to contaminate the other.
Write It Down and Check It
Whatever convention is chosen, it needs to be recorded in the trading plan and verified whenever a platform updates or a new workspace is built. It takes one glance at a known level to confirm. Most of the strange level disagreements that turn up in a review are this setting, and finding it after the fact costs far more than the check does.