How do “read,” “skim,” and “glanced” categories get defined?

• Most ESPs classify reading activity using time based thresholds.
• Glanced means opened for only a few seconds.
• Skimmed means opened long enough to scroll or scan.
• Read means the message remained open for a longer sustained period.

Each provider uses different thresholds. Some define read as 8 seconds. Others require 15\. These categories are convenience labels rather than scientific measurements.