Birth Time Reliability is most useful when an accurate birth time is unavailable or uncertain. Maia Mechanics checks for changes before and after the entered birth time and shows how close the nearest change is. The closer the change, the more an error in the birth time could affect your chart.
To see it for your own chart, create a Maia Mechanics account and sign up for a free trial of the Essentials Plan or higher. Open your chart and go to Birth Data in the properties menu on the right.
Two reliability levels
Reliability is now shown separately for your foundational and your advanced properties, because they change at very different speeds. Each one is rated Low, Medium or High, based on how close the nearest change is to your birth time, whether earlier or later.
Foundational
Changes to any of these properties count toward foundational reliability: Type, Authority, Definition, Profile, Incarnation Cross, Centers and Channels.
Low: a change within 30 minutes of the birth time
Medium: a change within 31 to 120 minutes
High: no change for more than 120 minutes either side
Advanced
Changes to any of these properties count toward advanced reliability: Variable, Determination, Cognition, Environment, Motivation, Sense and Perspective.
Advanced properties change far more often than foundational ones. Cognition and Sense, for example, change roughly every 37 minutes. For that reason advanced reliability uses shorter time ranges:
Low: a change within 5 minutes of the birth time
Medium: a change within 6 to 15 minutes
High: no change for more than 15 minutes either side
It is common for a chart to have High foundational reliability and Low or Medium advanced reliability. This means your core chart is secure, but your advanced properties depend on a precise birth time.
The Birth Window
Below the reliability levels, the Birth Data tab shows a preview of the Birth Window: a timeline of your chart two hours either side of your birth time. Click the preview, or Open, to see the full view.
The full Birth Window covers 12 hours either side of your birth time and has two pages:
Properties shows every foundational and advanced property as a row on the timeline.
Activations shows all 26 Design and Personality activations, from the Sun to Pluto, in the same order as the chart columns.
Blocks that match your birth chart are highlighted, and blocks that differ are shown in grey. The cards at the top tell you how long your properties hold and when the closest change happens. You can switch between 2, 6 and 12 hours either side.
Hover over any block to see its value, its time range, how it compares with your birth chart, and which planet moved to cause the change. Click anywhere on the timeline to open the full chart for that exact moment. You can save that chart to your library.
Alternative birth time charts
A chart opened from the Birth Window is an alternative birth time chart. Birth Time Reliability is not shown for alternative birth time charts, because they are calculated at a specific moment chosen from the timeline rather than from a recorded birth time.