Horizontal balance. The middle three tiers show average electronegativity differences of approximately 2, 1, and 0. This sequence suggests a gradation or a descending trend from higher to lower differences. The value of 2 (tier 2) at one end and 0 (tier 4) at the other, with 1 (tier 3) in between, creates a kind of balanced sequence. The average of the extremes (2 and 0) is 1, which coincidentally matches the middle value.