There is an old joke about mixing herbicide and whether the mix requires 1 glug or 2 glugs when pouring the herbicide out of the jug. Estimating mixing by glugs is not the most effective form of measurement. There is, however, a label on every herbicide that tells you a proper rate to mix concentrate to water, to be most effective at killing what you're targeting. For example, selective herbicides are designed to kill broadleaf weeds in your lawn, without killing the grass. If mixed improperly, it can end up killing everything. So mix carefully.