Embodiments provide a handheld optical measuring device and method of measuring an optical property of a liquid sample. In some embodiments the optical measuring device includes a handheld controller module having an immersible sensor head and a sampling member including a sample cup and an attachment member that couples the sample cup to the handheld controller module. In some embodiments the attachment member is an elongated rigid member that is hingedly coupled to the controller module, thus providing a folding configuration for enclosing the sensor head with the sample cup during measurements, transportation, and/or storage. In some embodiments the attached sample cup provides a protective shell for the immersible sensor head during use and/or when not in use.