1881 July 7th. Born the youngest son of Gustav Horstmann, a clock and watch repairer who had located to Bath in 1854
c.1900 Worked for Bayntum Hippisley on the design of a single-cylinder three-wheel car
1901 Living at 6 Westhall Place, Bath. Louisa Horstmann (age 66 born Bath), Living on own means and a Widow. With her children Ida (age 39 born Bath), an Artist; Pauline (age 24 born Bath), a (?) Clerk; and Sidney Horstmann (age 19 born Bath), an Engineer. One visitor. 
1903 Showed a light car at the London Motor Show
1904 Established the Horstmann Gear Co to develop a variable speed gear-box he had invented. This was not a success but the company became well-known for its clockwork mechanisms and timers. He went on to make cars, producing about 1500 Horstmann Cars between 1913 and 1929. Around ten of the cars still exist.
1909 Married Frances Osbourne
1911 Living at 10 Norfolk Crescent, Bath (age 29 born Bath), a Motor Engineer, Maker and Employer. With his wife Frances (age 30 born Bath). Also his sisters Ida (age 49 born Bath), and Artist, and Anfritx(see note 1) (age 39 born Bath), a Miniature Paiinter. Also his cousin Catharine Knott (age 56 born Birkenhead), a Lace Expert and unmarried. 
1912 Birth of son Charles Edgar Ashton Horstmann who died a year later
1913 Formed Horstman Cars
1919 As Managing director of Horstman Cars, Sidney Adolfe Horstmann was awarded the OBE .
1962 July 11th. Died at Bath
Note 1. Known to be AUGUSTA Louisa Horstmann.