A wavemeter for determining a wavelength of an incident optical beam comprises four optical components, each being arranged in the incident optical beam or in a part of it, providing a path with a respective effective optical length, and generating a respective optical beam with a respective optical power depending on the wavelength of the incident optical beam. The example of the medium has a recording layer containing a three dimensionally cross-linked polymer matrix including an epoxy resin, a radically polymerizable monomer, and a photo radical polymerization initiator. To carry out a contactless distance measurement in accordance with the pulseecho method in the interior space of the air spring, an ultrasonic transmitterreceiver is mounted on one of the two connecting parts and a reflector is provided on the other one of the two connecting parts. The altered data can then be inverse-transformed, and inverse-permuted, to return same to substantially its original form. The weight of the core is reduced in order to produce an overall golf ball which meets, or is less than, the 1.