Two currencies can be flat against each other in nominal terms while their real relationship moves a long way. If domestic prices rise faster than foreign ones and the nominal rate does not adjust, domestic goods become expensive abroad and the currency has appreciated in real terms without moving on the screen.
This is the gap a crawling-peg is designed to manage, and it is the reason an unchanged peg becomes untenable in a high-inflation economy: the real rate drifts until the trade balance breaks.
The real rate is a better guide to trade flows than the nominal one and a worse guide to short-term price action, since capital flows dominate over horizons a trader cares about.
Example: nominal rate unchanged over a year, domestic inflation 8%, foreign inflation 2%. The currency has appreciated about 5.9% in real terms, so exports are meaningfully less competitive than the chart suggests.
Related: real-effective-exchange-rate, purchasing-power-parity, crawling-peg, terms-of-trade