Preview a proposed rule against relevant events before you turn it on. A preview describes which events match and which configured actions would apply. It reads stored snapshots. It does not write.
When more than one calendar is in play, each row names the calendar the event is on. Travel, buffers, and holds that other rules would put around an event show as context, so you can see the week as it would look.
Every travel figure Google measured carries this line: Travel times and distances from Google Maps. Fixed-length travel configurations do not use Google’s measurement, so they do not carry that line.
Preview is not the same as turning a rule on. A draft stays a draft until you switch it on in Heldrey. Set up a rule from an assistant follows the same split: the assistant can preview; you turn the rule on.