here is the anita 811 from 1974 by sumlock comptometer ltd,
similar to the 810 but with a memory. a
switch is required to activate the memory which then accumulates a total
whenever equal is pressed. rm recalls the memory value and if
switched off, the memory retains its value throughout further calculation.
this appears to be the only point of the switch.
the design is rather nice, cool 70's retro with a red led display and
brushed aluminium back that slides off to reveal a battery compartment that holds three AA cells. a socket in the top of the unit accepts the
optional mains adapter.
the unit operates in a manner unconventional today. calculation is
performed like a desk calculator so that 2+3+ adds 2 and 3 (rather than
2+3=). equals is for multiply, so that 2*3=+4+ performs 2*3+4=. this seems
a bit odd at first, but it can lead to some useful optimisations. the
later, scientific 841 did not operate this way.
here is also the anita rounding feature activated by the switch
with the rounded logo. in this mode, all calculations round to two decimal