In droplet deposition apparatus comprising one or more independently actuable ink ejection chambers, electrical signals are applied to reduce variation in the temperature of the droplet fluid between chambers and with variations in droplet ejection input data. The compression body is composed of a material containing voids, and has a compressive strength of at least 1 MPa and a void fraction of between 10% and 90% of its total volume. If the cancelling drive member rotates, an elastic pressure portion of the deflectable spring member is brought into contact with the first biasing contact portion. The eyewear still further includes a pair of auxiliary lenses with at least one fourth mating surface that is removably secured to the second mating surface by magnetic attraction. The amplitude of the resulting sinusoid is used to estimate a distance to an interface in an earth formation. A second elongated aperture and a second slit traverse through the second plate.