commodore sr-9190r

altogether more competent than the sr-4140r. it has 49 buttons as well as both `f' (for 2nd function) and `(inv)' keys for extra functions. parentheses nest to three levels (as indicated on the keys) and there are nine memories, although some are used as workspace for certain operations. 

this model has some unusual and interesting functions like ln(gamma(x)) and probability distributions such as binomial, normal and poisson. there is also an integration key. this does not integrate a formula because there is no way to program the unit. instead it implements the trapezoidal rule but manually; you have to input the x and y values of the function and it does the adding, which is rather novel. some complex number support is available. above + - * /, there are j+, j-, j*, j/, which perform arithmetic basics.

statistics is rather good, not only are there the aforementioned probability distributions, but 2d stats and linear regression are here. memories 1-6 are used for the partial sums. there is even room for several common and useful unit conversions in both directions.

for example the gauss function calculates the normal probability function, defined by one of the few other machines to offer this is the hp32e. accuracy is good, agreeing with the 32e.

it is powered by 3 AA internal rechargeable cells. these are normally dead and should be removed before they leak and corrode the circuit. without the internal cells, use a 5 or 6v mains adapter (not 9v). see inside for wire details.