Patterns are written in UK crochet terms, however the e-book does give the corresponding US terms in the introduction.

Actual hook size was a 2.5mm hook, which is between a B1 and C2 hook.

Gauges vary by design
Yardages vary by design

1 ball of each color was used to make all five mandalas as shown.

Colors used:
Schachenmayr Catania
A. Jade 00253
B. Paprika 00390
C. Turquoise 00146
D. Royal 00201
E. Gold 00249
F. Sand 00404
G. Apple 00205
H. Sea Green 00241
I. Bittersweet 00415
J. Orchid 00222
L. Claret 00192
M. Sky 00247
N. Fuchsia 00128
(there is not a color for K.)