|the el-5103 is probably sharp's finest pocket
scientific model and ahead of its time in many ways. its a fairly rare
machine appearing briefly in the gap between their older scientific
models like the el-512 and the later basic
programmable pocket computers like the pc-1251.
a very nicely designed machine and a pleasure to use, small, slim and
pocket sized. the buttons are excellent and the display is an alpha
numeric, dot-matrix. this was a rarity in calculators of its time and the
only other alpha capable machines nearby were the
hp41c and casio fx-602p. the sharp's alpha
capability is limited, however, because it is not truly programmable.
the true purpose of the alpha numeric display is formula entry and in
this regard makes this machine one of the earliest formula entry models.
the formula expression evaluation of up to 80 steps is superb, with implied multiplication
for brackets and number prefixes to functions. for example 2sin1,
2(3+√5) and 1÷2π all do the expected thing. rather than
having an ans key (like today), the last expression can be
recalled with PB (playback) and re-edited, then re-evaluated.
this does create a difficulty because you cannot immediately operate on
a previous result (like you might today press √ ans).
although not truly programmable, several early and pioneering
versions of expression programming are available. a
selector switch chooses between AER (algebraic expression
reserve) and COMP modes. these parallel the concepts of program
and run modes on programmable machines. in AER mode a (single)
expression of up to 48 steps involving variables A-E and M
can be accommodated. on switching back to comp mode, the
expression can be evaluated in terms of the current contents of the
variables by pressing the COMP button. another variant allows an
expression to be reserved as a function of given variables. for example
f(AB) = √(A² + B²) defines a function of two unknowns A
and B. in comp mode, the COMP button will prompt the user
for values of the unknowns then proceed to evaluate the expression. this
is a bit like the function library of the casio
fx-5000f and fx-50f. the reserve expression
can have multiple parts separated by comma.
the rest of the features are a familiar set of scientific functions
including hyperbolics and 2d stats. the stats is a special mode (on the
switch) that reassigns the A-E memories to stats storage.