El Bar Americano en España by Pedro Chicote (1927, p.61)

0.75copita de gin — Source omits the unit and uses shorthand notation.base
ice — 4 ó 5 pedacitos de hielobase
0.33— de vermut Carpano amargo — Source omits the unit and uses shorthand notation.modifier
  1. Agítese muy bien y sírvase en copa de cocktail.

Ice: Ice

Cocktails by Pedro Chicote (1928, p.168) — Carpano amaro branch

0.75 copitagin base
0.33 copitaBitter vermouth — Vermut Carpano amargomodifier
  1. Shake very well and serve in a cocktail glass.

Ice: 4 to 5 pieces ice

This matters because it preserves a stripped gin-and-bitter-vermouth aromatic in the Madrid field.

See also: Martini Cocktail, Italiano Cocktail