Taiwan Adjusted Price — an adjustment for comparability, never a traded price
The dangerous misreading of an adjusted series is that it shows what a share cost at the time. It does not, and never did. Adjustment is a purely mechanical operation: events that move the quoted price without changing a holder's wealth — dividends, splits, capital reductions — are removed from the series so that returns become comparable across periods. The resulting figures never traded on any day. It is a ruler for measuring return, not a photograph of history, and treating the ruler as the photograph is exactly the error this page exists to prevent.
What adjustment does and why it is needed
On an ex-dividend day the quote falls while the holder receives cash; on an ex-rights day it falls while the holder receives shares. The price moved, the wealth did not. An unadjusted series records those drops as returns and systematically understates long-run performance. Adjustment removes them mechanically using published distribution data, and every adjustment is returned with its event date, category, factor and inputs — no invented coefficient, no smoothing, no hidden parameter.
The baseline and method are always disclosed
A series can be adjusted backwards from the latest day or forwards from a historical reference date. The absolute numbers differ while the return series is identical — both are correct, they simply anchor elsewhere. We therefore disclose the baseline date, direction and method on every response and return the unadjusted close alongside. Two sites disagreeing usually means two baselines, not an error; an adjusted price without a disclosed baseline cannot be verified at all.
What an adjusted figure must not be used for
It must not be checked against contemporaneous news prices or a personal fill — those are raw prices and were never meant to match. It must not be multiplied by the share count to produce a historical market capitalisation; use the raw close for that. It must not be used to back out an ex-rights reference price or a daily limit. Where the question is “what did it cost that day”, the raw close is in the same response, and we do not choose between the two series for you.
Data state and what this page does not do
Distribution and capital-change events come from official filings, gated at publication time; where an event needed for an adjustment is not yet published the affected span is marked undetermined with the missing item named, never substituted with an estimated factor. Output is deterministic for identical inputs. The page makes no price projection, issues no signal or target price, publishes no ranking and no stock list — comparability of returns is where its job ends.