Intermix ratio
The intermix ratio, also known as the matter-antimatter ratio, was the ratio in which matter and antimatter were combined. A warp core is the most familiar device in which the intermix ratio was essential. 

Following its expedited launch during the V'ger incident, the warp core of the refitted  required new fuel equations to balance the intermix. The essential simulation of the flow sensors was bypassed resulting in an antimatter imbalance. ()

In the 2364 Starfleet Academy entrance exam, one of the questions dealt with intermix ratios: 
"The matter and antimatter tanks on a  starship are nine-tenths depleted. Calculate the intermix ratio necessary to reach a starbase one hundred light years away at warp factor 8." 
This was a trick question as there was only one ratio with matter/antimatter: 1:1. ()

In the same year, after the Shuttlecraft 13 crashed on Vagra II, the  was rushed to have warp drive operational. In the start-up sequence, prior to powering up the engine core and injecting reactants, the matter-antimatter injectors were primed to a ratio of 25:1. Minimal warp speeds were recommended, however Captain Jean-Luc Picard ordered warp 8. ()

In 2367, Doctor Leah Brahms was surprised that Geordi La Forge had changed the intermix ratio from Starfleet regulations. He explained that experience told him it needed to be a little lower to be more efficient. ()

In 2369, when bluffing the Ferengi Morta with a nonsensical description of the technology on the Enterprise-D, Commander William T. Riker told him that the ramistat kiloquad capacity was a function of the square root of the intermix ratio times the sum of the plasma injector quotient. ()

In 2373, Jadzia Dax ordered the intermix be manually set to 0.01, prior to the warp chamber initialization, on the  after it had been damaged by a cascade virus. ()

See also
Intermix formula
Measurements