An apparatus for performing a light-absorption measurement of a specified amount of sample subject to pressure force, the apparatus comprising: a surface configured to receive a sample thereon; a light reflector mechanically coupled with the surface and separated from the surface by a separation distance; an actuator connected to at least one of the surface and the light reflector to change the separation distance, while the light reflector remains mechanically coupled with the surface, to a first separation distance and to a second separation distance different from the first separation distance; a first stopping member arranged to stop a first change in the separation distance at the first separation distance; and a second stopping member arranged to stop a second change in the separation distance at the second separation distance; wherein a mechanical coupling between the light reflector and the surface includes a base member, a housing, a sample link member having a first end and a second end, a rotatable shaft of the actuator, the rotatable shaft having a first cam profile and a second cam profile, and a light reflector link member having a first end and a second end, wherein the surface is an upper surface of the base member, the base member is in contact with the first end of the sample link member, the second end of the sample link member interacts with the first cam profile of the rotatable shaft, the rotatable shaft is fixed to the housing and is rotatable relative to the housing, and the light reflector link member is fixed to the light reflector; wherein when the rotatable shaft is oriented in a first orientation, the mechanical coupling between the light reflector and the surface includes the housing, the housing contacting an upwardly-facing surface of the light reflector link member; and wherein when the rotatable shaft is oriented in a second orientation, the mechanical coupling between the light reflector and the surface includes the second cam profile of the rotatable shaft, the second cam profile interacting with the first end of the light reflector link member. a surface configured to receive a sample thereon; a light reflector mechanically coupled with the surface and separated from the surface by a separation distance; an actuator connected to at least one of the surface and the light reflector to change the separation distance, while the light reflector remains mechanically coupled with the surface, to a first separation distance and to a second separation distance different from the first separation distance; a first stopping member arranged to stop a first change in the separation distance at the first separation distance; and a second stopping member arranged to stop a second change in the separation distance at the second separation distance; wherein a mechanical coupling between the light reflector and the surface includes a base member, a housing, a sample link member having a first end and a second end, a rotatable shaft of the actuator, the rotatable shaft having a first cam profile and a second cam profile, and a light reflector link member having a first end and a second end, wherein the surface is an upper surface of the base member, the base member is in contact with the first end of the sample link member, the second end of the sample link member interacts with the first cam profile of the rotatable shaft, the rotatable shaft is fixed to the housing and is rotatable relative to the housing, and the light reflector link member is fixed to the light reflector; wherein when the rotatable shaft is oriented in a first orientation, the mechanical coupling between the light reflector and the surface includes the housing, the housing contacting an upwardly-facing surface of the light reflector link member; and wherein when the rotatable shaft is oriented in a second orientation, the mechanical coupling between the light reflector and the surface includes the second cam profile of the rotatable shaft, the second cam profile interacting with the first end of the light reflector link member.