The butterfly compensation switch was a control found on TARDIS consoles.
The Fifteenth Doctor belatedly switches the butterfly compensation back on. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])
The switch appeared on the Fifteenth Doctor's console as a blue switch on the panel facing the TARDIS doors. When the Fifteenth Doctor was getting used to his controls, he forgot to set the switch and so encountered the butterfly effect when Ruby Sunday stepped on a butterfly. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])
Devices which regulated the "causalness" of a time traveller, including what effect or lack thereof stepping on a butterfly might have, were termed "chaotic limiters" by The Book of the War. (PROSE: The Book of the War [+]Loading...["The Book of the War (novel)"])