Marie Crous

She was the tutor of Charlotte de Caumont La Force,[1] a girl from a noble Huguenot family, and enjoyed the patronage of the salonnière Madame de Combalet, the Duchess d'Aiguillion, a niece of Cardinal Richelieu.

The Advis includes a presentation of decimal fractions, based on Simon Stevin's work De Thiende.

She introduced a change from Stevin's work: the introduction of a period (now a comma in many countries) to separate the units from the decimal part, and the zero to indicate that a given position is empty.

The Advis is dedicated to her pupil Charlotte de Caumont La Force.

In the preface to the Advis, she proposed the introduction of a decimal metric system of weights and measures in France; this would not happen until the end of the eighteenth century.