VOLUME: More turn makes more loud.

TEXTURE: The Merkin is composed of three gain stages, and only the first two are governed by the Texture knob. This knob essentially functions as a mixer control between the first stage and the first and second stages combined. The output is then sent to the final stage, which is saturated by the chosen configuration. When this knob is set halfway, some mild phase cancellation can be heard (or not heard, as the case may be), delivering some extra vintage character.
The Merkin Fuzz accepts anything between 9V and 18V with a center-negative DC power supply. Plugging in anything other than this (center-positive, AC, higher voltage, etc.) there’s a good chance that you can kiss your Merkin goodbye. Save yourself some time and headache and plug the correct adapter into the pedal the first time, otherwise you run the risk of voiding your warranty, and there’s no romance in failure.