Double prefixes have been used in the past, such as micromillimetres or "millimicrons" (now nanometres), micromicrofarads (now picofarads), kilomegatons (now gigatons), hectokilometres (now 100 kilometres) and the derived adjective hectokilometric (typically used for qualifying the fuel consumption measures) [REF].
In 2010, UC Davis student Austin Sendek started a petition to designate "hella" as the SI prefix for one octillion (1027) [REF].