Long exposures need more time than the meter says. This uses each film's own datasheet: a formula when the manufacturer gives one, its table otherwise. Nothing is extrapolated past the published times.
Calculate
Metered 30 s
Not published
The datasheet doesn't cover a metered time of 30 s, and rolllog doesn't extrapolate. Bracket and test.
ADOX CMS 20 II: datasheet values
Metered
Open up
Or expose
1/1000 s
+0.67 stops
—
1 s
+0.67 stops
—
10 s
+1 stop
—
Source: ADOX Fotowerke CMS 20 / ADOTECH II datasheet (2014-10)