Indications and reflective prisms
The bi-directional jumping hour and trailing minute displays on HM8 are materialised by overlapping discs (one for the hours, one for the minutes), completely covered in Super-LumiNova. The effect of large numerals is created by masking all of the lume except for the numbers.
The discs rotate horizontally on top of the movement; they are visible in the corners of the transparent Engine cover. Yet the time indications are displayed vertically in a ‘dashboard’ at the front of the case. To achieve this, MB&F worked with a high-precision optical glass supplier to develop reflective sapphire crystal prisms that reflect light from the discs 90°. The prisms also magnify the indications by 20% to maximise legibility.
HM8 has separate sapphire crystal prisms for the hour and minute displays, which are wedge-shaped with precisely calculated angles to ensure that light is reflected (and reversed) from the horizontal indications to the vertical rather than refracted (bent). A convex lens at the front provides the magnification.
Sapphire crystal is much more difficult to work to optical precision than glass, and it took considerable development and meticulous care in production to create crystals that reflected and magnified light without the slightest distortion. Because the time is reflected, the numbers are printed on the discs as mirror images so that they display correctly on the ‘dial’.
The vertical, forward-facing display makes HM8 Can-Am an excellent driver’s watch, as there is no need to lift your wrist from the steering wheel to read the display.