A head mounted display to be worn by a user, comprising: an adjustable crown band; a crown band circumference adjusting mechanism coupled to the adjustable crown band and configured to adjust a circumference of the crown band to releasably secure the crown band to the crown of the user, the crown band circumference adjusting mechanism comprising: a first housing mounted at a posterior end of the HMD, the first housing including a first knob and a first pinion rotatably coupled thereto; and left and right crown racks mounted at posterior ends of the adjustable crown band, the left and right crown racks passing through the first housing and engaged to the first pinion wherein rotating the first pinion via the first knob adjusts a length of the left and right crown racks passing through the first housing to adjust the circumference of the crown band; an armature including a left arm and a right arm (3752, 3754), each of the left arm and the right arm mounted at a respective proximal end to corresponding left and right attachment structures on the HMD; a display mounted at left and right sides to respective distal ends of the left and right arms (3752, 3754); and an eye relief distance adjustment mechanism configured to move the left and right arms (3752, 3754) in a timed manner toward and away from the crown band along a substantially linear path when a pushing or pulling force is applied to the display by the user, to thereby adjust an eye relief distance from the display to an eye of the user when the crown band is fitted on the crown of the user, wherein the eye relief distance adjustment mechanism comprises: left and right eye relief bands (150, 152) including the left and right attachment structures, the left and right eye relief bands extending posteriorly from the left and right attachment structures respectively and passing through the first housing, the left and right eye relief bands each including an eye relief rack engaged to the first pinion, wherein rotating the first pinion via the first knob adjusts a length of the left and right eye relief racks passing through the first housing to move the left and right arms in the timed manner. an adjustable crown band; a crown band circumference adjusting mechanism coupled to the adjustable crown band and configured to adjust a circumference of the crown band to releasably secure the crown band to the crown of the user, the crown band circumference adjusting mechanism comprising: a first housing mounted at a posterior end of the HMD, the first housing including a first knob and a first pinion rotatably coupled thereto; and left and right crown racks mounted at posterior ends of the adjustable crown band, the left and right crown racks passing through the first housing and engaged to the first pinion wherein rotating the first pinion via the first knob adjusts a length of the left and right crown racks passing through the first housing to adjust the circumference of the crown band; a first housing mounted at a posterior end of the HMD, the first housing including a first knob and a first pinion rotatably coupled thereto; and left and right crown racks mounted at posterior ends of the adjustable crown band, the left and right crown racks passing through the first housing and engaged to the first pinion wherein rotating the first pinion via the first knob adjusts a length of the left and right crown racks passing through the first housing to adjust the circumference of the crown band; an armature including a left arm and a right arm (3752, 3754), each of the left arm and the right arm mounted at a respective proximal end to corresponding left and right attachment structures on the HMD; a display mounted at left and right sides to respective distal ends of the left and right arms (3752, 3754); and an eye relief distance adjustment mechanism configured to move the left and right arms (3752, 3754) in a timed manner toward and away from the crown band along a substantially linear path when a pushing or pulling force is applied to the display by the user, to thereby adjust an eye relief distance from the display to an eye of the user when the crown band is fitted on the crown of the user, wherein the eye relief distance adjustment mechanism comprises: left and right eye relief bands (150, 152) including the left and right attachment structures, the left and right eye relief bands extending posteriorly from the left and right attachment structures respectively and passing through the first housing, the left and right eye relief bands each including an eye relief rack engaged to the first pinion, wherein rotating the first pinion via the first knob adjusts a length of the left and right eye relief racks passing through the first housing to move the left and right arms in the timed manner.