You will find two sets of letter number pairs separated by a colon in the bottom right hand corner on the bottom label of the SpectroVis Plus (SVIS-PL, discontinued).
The letter and number pairs correspond to the firmware and hardware revision of the device.
The H stands for the hardware revision. For example, H:2 means that the device is second generation hardware.
The F stands for the firmware revision. For example, F:2 means that second generation firmware is installed on the device.
If your SVIS-PL does not have a set of letter and number pairs in the bottom right hand corner of the bottom label then it is a first generation SVIS-PL
SVIS-PL units with F: 2.5 have intensity correction as a selectable feature in Intensity mode