A handheld optical testing instrument configured to rest on a surface and shaped to be held by a user, the optical testing instrument comprising: a shell defining a cavity for receiving a sample tube, wherein the cavity is configured to support the sample tube in an upright position in an instance in which the optical testing instrument is in a testing position, the shell comprising a bottom shell surface, wherein the bottom shell surface comprises: at least one support element, wherein the at least one support element is configured to engage the surface to support the optical testing instrument in a testing position; and a translational surface configured to engage the surface to support the optical testing instrument in an angled position, wherein the optical testing instrument is shaped to be held by a user about the shell such that the user can hold the sample tube upright within the optical testing instrument during handheld operation, wherein in an instance in which the optical testing instrument receives a sufficient lateral force, the optical testing instrument is arranged to tilt from the testing position to the angled position to cause the translational surface to engage and slide relative to the surface to prevent the optical testing instrument from tipping past a point where the optical testing instrument tips over such that the optical testing instrument is arranged to return to the testing position in an instance in which the lateral force is removed and wherein, in both the testing position and the angled position, a center of gravity of the optical testing instrument is disposed above points on the surface that are radially inward of an engagement point of the translational surface that engages the surface. a shell defining a cavity for receiving a sample tube, wherein the cavity is configured to support the sample tube in an upright position in an instance in which the optical testing instrument is in a testing position, the shell comprising a bottom shell surface, wherein the bottom shell surface comprises: at least one support element, wherein the at least one support element is configured to engage the surface to support the optical testing instrument in a testing position; and a translational surface configured to engage the surface to support the optical testing instrument in an angled position, at least one support element, wherein the at least one support element is configured to engage the surface to support the optical testing instrument in a testing position; and a translational surface configured to engage the surface to support the optical testing instrument in an angled position, wherein the optical testing instrument is shaped to be held by a user about the shell such that the user can hold the sample tube upright within the optical testing instrument during handheld operation, wherein in an instance in which the optical testing instrument receives a sufficient lateral force, the optical testing instrument is arranged to tilt from the testing position to the angled position to cause the translational surface to engage and slide relative to the surface to prevent the optical testing instrument from tipping past a point where the optical testing instrument tips over such that the optical testing instrument is arranged to return to the testing position in an instance in which the lateral force is removed and wherein, in both the testing position and the angled position, a center of gravity of the optical testing instrument is disposed above points on the surface that are radially inward of an engagement point of the translational surface that engages the surface. <EOS>