Building a Stat Comparator That Refuses Invalid Deltas

A comparison table becomes dangerous when it produces a precise-looking answer for values that were never comparable. I ran into this while implementing a Gear comparison view. Each item could expose base stats and inherent modifiers. Values could be flat numbers, percentages, or per-second rates. Either side could also omit a field entirely. The tempting implementation was to join rows by the visible label and subtract right from left. That would have allowed a flat Attack Damage value to collide with an Attack Damage percentage, and it would have encouraged treating a missing value as zero. The safer implementation turned out to be a small Map keyed by three pieces of semantic identity. Model the comparison result explicitly The result row needs to preserve more than two numbers: type StatSource = "base" | "inherent"; interface ComparisonRow { key: string; label: string; source: StatSource; unit: "flat" | "percent" | "per-second"; left: number | null; r