Read the perimeter clockwise
Starting at the left, age 0 uses A. The upper-left corner at age 10 uses F. The top at age 20 uses B. Age 30 uses G, age 40 uses C, age 50 uses H, age 60 uses D, and age 70 uses I. Age 80 returns to the left anchor.
For 15 May 1990, the decade values are 15, 20, 5, 6, 19, 4, 12, 9, then 15. The numbers come from the same core chart. They are not recalculated from the calendar year.
Decades are a symbolic overview
Some schools add smaller age intervals by recursively combining neighboring values. Their interval labels and rules can differ. Our overview exposes only the decade positions for which its formula is displayed.
A broad interval cannot tell you when you will meet a partner, change jobs, become ill, or receive money. Interpreting it as a scheduled event adds a claim that the arithmetic does not support.
Look backward with care
It can be interesting to compare a decade theme with your notes from that period. Be aware that broad symbols can fit many events after the fact. Record the details that do not fit as well as those that seem meaningful.
Your understanding of an earlier period may change as you learn more. The chart’s static number does not freeze the meaning of that period or establish why an event occurred.
Use the next stage as a question
Rather than asking what must happen next, ask which habits or values you want to carry forward. Choose an action based on your current circumstances.
A hopeful theme might inspire a goal; a structure theme might suggest a routine. Either action can be evaluated on its own merits. The chart does not make the outcome inevitable.
A question to carry with you
What part of this reflection can I check against my own experience?
References & context
References for the calculation method and Arcana tradition.