Vol GK
Definition / Formula
Vol GK = sqrt( mean GK of the last 12 closed 5-minute bars
/ median, across previous days, of each day's 12-bar mean GK )
Each bar’s GK is the Garman–Klass variance ½·ln(High/Low)² − (2·ln2 − 1)·ln(Close/Open)², plus the opening jump ln(Open / previous Close)² when the previous bar opened 5 minutes earlier.
Window: the 12 bars ending at the current bar. During a session it is anchored on the session open: each previous day uses the bars at the same offset from that day’s own open, so daylight-saving changes stay aligned. In the first 55 minutes after an open, the window includes bars from before the open. Outside every session the window is the last 60 minutes, compared with the same 60 minutes on previous days (24/7 fallback).
1.0x = as volatile as a typical day at this time. 2.0x = twice as volatile.
Previous days: up to the last 20 previous weekdays (19 weekend days for crypto on weekends), since today is one of the 21 / 20 days loaded. At least 10 complete windows are needed. The median keeps one news day from moving the baseline.
No value (empty cell): fewer than 10 complete windows on previous days (a symbol listed recently), a missing bar in today’s window, or no trades in the whole window (all 12 bars flat, so today’s mean is 0). On the first day of the calendar (Monday; Saturday and Sunday for crypto on weekends), the first 55 minutes of the Tokyo session also show no value: their window reaches into the previous day, which is not part of the calendar.
Session closed: only TradFi on the weekend calendar shows a dim — with the next session open. Outside the sessions (crypto at any time, TradFi on weekdays), the cell shows the 24/7 fallback value instead of a dash.
UI Breakdown
The track uses a log2 scale from 0.25x to 4x: 0.25x and below is an empty track, 0.5x fills a quarter, 1.0x fills half, 2x fills three quarters, and 4x and above fills the track. A half-full bar is normal for this time of day. There is no marker and no colour band. The value, rounded to two decimals (e.g. 1.12x), sits to the right of the track. The cell’s tooltip shows the value to three decimals and whether it uses the session window or the 24/7 fallback.
| Control | Action | Effect |
|---|---|---|
| Column header | click | sort descending (largest first); click again to flip |
Value Ranges
| See | Value Band | Status | Visual Appearance |
|---|---|---|---|
 | Below 1.0x | Quieter than usual | Bar under half |
 | 1.0x | Typical for this time of day | Bar half full |
 | Above 1.0x | More volatile than usual | Bar past half |
 | 4x and above | Full scale (4x or more) | Full bar |
 | Fewer than 10 complete past windows, or a missing bar today | No value | Empty cell |
 | Session closed | Market closed | Dim dash |
Summary: Vol GK compares how much price moved over the last 12 five-minute bars with how much it usually moves over the same bars on previous days.