sharp micro compet qt-8d

the micro compet from 1969 was a breakthrough, the first use of LSI (large scale integration) enabled this machine to be substantially smaller than its predecessors and those of other manufacturers like the anita. although not yet compact enough to be battery powered, there is a retractable carry handle in the top so the unit could easily be transported in a briefcase.

units like this, with the use of new LSI, marked the start of the calculator wars. a time when many older manufacturers like busicom and sumlock were forced out of business.

this model powers up scrambled. the digits dance and flicker erratically. after a couple of presses of the C key, it calms down and is prepared to calculate. calculation proceeds like most desk calculators where the operation is postfix. for example 2+3 is entered as 2,+=,3,=+ and 2-3 as 2,+=,3-=. multiply works in the normal way, except divide is rather strange. it shares the same key as multiply, and to perform a divide you finish with the red subtract button. for example 2*3 is entered 2,*/,+= but 2/3 is 2,*/,-=.

the display is rather unique and of a highly styled design. zero is only half height (like early casios). it consists of 8 individual 8 segment (plus point) Itron display tubes. there is a special ninth tube on the right capable only of a minus sign and a dot (which indicates overflow).

compared to models of this period, this one calculates very fast. i see only momentary delay for multiply and divide operations. some models could easily take half a second.

you can see that only some of the segments are shared. for example the slant of the six, two, seven and eight are the same, but not the 4 or the 1, which use more upright segments.
inside the layout is neat, there is a display circuit board and a processor board.
here is the cpu board. there are four LSI processors made by rockwell. having 4 chips was common in these early days (see also the casio as-l). was it one for each of + - * /  or is that too simplistic.
the keyboard is marvellous. it works by magnetic reed switch proximity. this design make it almost indestructible because there is no electronic contact made by the key movement directly, only indirectly. if necessary lubricate the keys with precision teflon grease.