The hours
The US premarket is the session before the cash open. Prints can start near 4:00 ET. The cash session runs from 9:30 ET to 16:00 ET.
A price before the open is not the official close. The open is its own auction at 9:30 ET.
Thin prints
Fewer shares change hands than during the day. One print can move the shown price a long way. The bid and the offer can sit far apart, so the last print is not always a price you could have traded.
How to read a print
If you compare a premarket print with the day before, use the prior regular-session close. Name both prices. If one is missing, skip the comparison.
A halt can stop prints before the open. The exchange notice is the source for the reason and the resume time.
General market news. Not investment advice. The author may hold the Runner Flag name and does not trade it before the 9:30 ET open on the publication day.