Fortis is a great renown company and offers many choices in every type of professional use. This watch is quite rare and they are a very cool conversational piece. The watch is serviced and works well including its revolving inner bezel/compass. 
 
Details:
 
Brand: Fortis
Model: Easy-Math
Reference: 7242
Year: 1960's
Material: Stainless Steel
Dimensions:  38mm
Crystal:  Plexiglass
Movement: Manual Wind
Bracelet/Strap: Hirsch Leather Band
Box/Papers: No/No