Optical Square by Kilpatrick and Co London.
Although there are several references to Kilpatrick and Co in Melbourne between 1853 to 1925 there is very little information about the business in London.
I would estimate that this instrument would be circa 1890.
MDS Optical Square
Couldnt find much on this London Manufacturer when searching the Web.
Optical Square by Otto Boettger
Otto Boettger 88 Flinders Street, Adelaide. South Australia first established in 1877 and was still in business in the 1960s
Optical Square by Salmoiraghi
This optical square is tiny and simple.
It is engraved " Ing.A.Salmoiraghi & Co, Milano"
I estimate that this is circa 1900.