He named these various four-day sets "Galactic Activation Portals."
On the grid map below DR. ARGÙELLES paired up the first and last days, days #1 and #20, along with days #241 and #260. These four days are on 'the corners' of the 260 grid-map shown below. If one adds up those four weekday numbers (1-13) the total equals 28.
1 + 7 + 7 + 13 = 28
The next 2 pairs (that add up to 28) occur in rows 2 and 12, and so on.
He designated the dark grey shaded days on the chart below as connected to "The Past" or first half of the 260-days and the brown shaded days connected to "The Future" or last half of the 260days.
260-Day Map with Galactic Activation Portals (G.A.P.)
Past (grey) and Future (brown)
"Key" square at the very top of the Aztec Calendar.