here is the advanced scientific calculator
model 1540 from 1976.
this mains desktop model with a ten digit vacuum fluorescent display
appears to be functionally identical to the sr-1800. indeed, both have the
same chipset, the ghu-03a and give the same results.
the small buttons
are a bit fiddly to use considering the size of the machine, the layout is
slightly peculiar and the equals button would benefit from being bigger.
display is clear and it uses 12 digits internally. results are similar to
the sr4148r and it shares many of the same
features, like the radians dot, exponent scaling and two memories.