The two overseas lines of SK Hynix, normalized to one Korean common share in USD. The premium is only computed when both lines are actually trading; when their sessions don't overlap, the ratio is frozen.
Both converted to what one Korean common share is worth, in USD.
Computed only during the SKHY ∩ HY9H overlap; frozen (held flat) otherwise.
Nasdaq ADR, extended hours. Solid = trading, dashed = frozen (held).
Frankfurt GDR. Solid = trading, dashed = frozen (held).
Each ADS is one-tenth of a Korean common share (10 ADS = 1 share); each GDR is one full share (1 GDR = 1 share). Both are expressed as the USD value of one Korean share.
Overlap & freezing. A 15-minute bar is live only if both SKHY and HY9H printed within ±45 minutes of it — i.e. both venues are actually trading (extended and overnight sessions included). When only one side is open (or both are closed), the premium is frozen: the last both-open ratio is held flat and drawn dashed. This avoids a fake premium from one leg moving while the other's price is stale. GDR ratio assumed 1:1.
Prices. Each quote uses the latest actual print including pre-market and after-hours; Yahoo's free feed does not carry the overnight ATS session, so overnight the freshest value is the 8pm ET after-hours print (then treated as stale/frozen).
A big ADR premium can be real. SKHY (the Nasdaq ADR) has at times traded well above the Korean shares and the GDR because US demand outruns the friction of converting ADRs back to Korean stock. So a double-digit SKHY-over-HY9H premium is not necessarily an error — but a reading taken when one leg is stale is not a clean number, which is why the chart freezes outside the overlap.
Two currencies. The comparison rides on EUR/USD; an FX move alone can shift the premium.
New listing. SKHY is recently listed, so the 15-minute history is short and grows each session. Data is free/delayed and refreshes every 10 seconds while this tab is open — informational only, not tradable.