[General Topics] Skyica:
Scientific calculator plus 991​

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This app stands out with very extensive and quite powerful calculation functionality.

However, it has some worrying bugs (see below).

Simplification and symbolic integration seem to be very good, but there are problems with equation solving and minima / maxima finding. Its statistics features are quite comprehensive.

2D graphing is good but has inconveniences. 3D graphing is missing.

The user interface is sophisticated, but some functionality is not well organized and documented, and there are many inconveniences.

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Numeric and symbolic calculation​

Symbolic computation essentials:

Feature Domain constraints, but they are not exploited sometimes, e.g., Ln(x*y)-Ln(x) with x>0 and y>0 is not simplified to Ln( y). (Input: Simplify(Ln(x*y)-Ln(x), x>0 and y>0))

Equation solving:

BUG When trying to solve an equation by just entering it or using SHIFT-SOLVE, inexact results are often returned, e.g., for sin(x) = x, something like [x=-0.0000083, x=-0.0000017] is returned. Using the Solve function, [x=0] is correctly returned.

BUG Even with Solve, equations involving periodic functions are often not correctly solved, e.g.:

For sin(x) = 0 only 0 is returned as solution; for sin(x) = cos(x) two complicated (although correct) numerical expressions are returned instead of the simple exact solution.

For sin(x) = x/2, sometimes [x=-1.89…, x=1.89…], and sometimes [x=0] is returned.

Feature Equation systems

Differentiation and integration:

Good Powerful symbolic integration, even some nonelementary integrals can be solved with special functions, e.g., logarithmic and exponential integrals and Fresnel integrals (however these functions cannot be plotted).

Also, for complicated integrals like x/(1+sin(x)), for the same input, sometimes operation is not supported is returned, and sometimes the correct solution.

Other calculus and analysis:

BUG Minima and maxima are often not correctly calculated, e.g., for x^4-x^2, only x=-1/4 is returned as minimum, for periodic functions also only one minimum and maximum is returned.

Bad No one-sided limits

Statistics and probability:

It may take some time to learn to use the statistics features, but they seem to work quite well.

Bad Data editor shows no row numbers.

Feature Extensive distribution calculation functionality with many distributions (I did not test this much).

Feature Statistical tests (at least in the Plus 84 83, see below)

Feature Confidence intervals calculations (at least in the Plus 84 83)

Feature It has hundreds of advanced functions that are named as in WolframAlpha and Mathematica, e.g., Series, Fourier, PowerExpand, ApplySides(~600 documented, ~300 I could find in the menus). However,

I did not test them and don’t know if they work reliably.

The inconvenience of the interface (e.g., that parts of expressions cannot be copied, and that equation systems must be entered in one line) makes more complicated calculations tedious, so that I question the usefulness of many of them.

The functions cannot be typed, and there is no alphabetic list from which they can be inserted.

Feature Programming:

It seems to have a full featured programming language that can interface the calculation functionality (

Symja

). However, the print function and graphics output seem not to work (only the result for the last line is printed automatically). Also, files cannot be saved.

2D and 3D graphing​

No 3D graphing.

Bad The functions to draw must be entered in linear form (i.e. not textbook form), or all in one line separated by :

Feature 3 workspaces

Graph types:

Feature Implicit plots

Display:

Bad Grid is quite coarse (and cannot be adjusted)

Navigation:

Feature Independent scale of axes

Bad No simultaneous pan and zoom with 2 fingers

Analysis:

Good Tracing is well implemented, tangent can also be shown

Good Derivative can also be shown, inflection points can also be shown

Environment and user interface​

Variables and functions:

Feature User-defined functions that can be used in numeric and symbolic calculations

Input and output:

Missing Parts of expressions cannot be selected and copied, only the whole input or result can be copied

Missing No undo & Redo

Feature Automatic calculation without tapping enter key

Feature Good “Quick Info”

BUG When copying expressions from the history, it often returns incorrect results, even if it retuned the correct result the first time the expression was entered.

Missing No import / export

Adaption and customization:

UI is good for both small and large phones, but not tablets

Feature Many high-quality themes

Bad Not convenient for symbolic computation, e.g.,

Variable x and equal sign are not accessible with one tap

For most symbolic computation one must switch between the main and a 2nd keyboard, whose keys are not well organized

Equation systems must be entered in one line

Documentation and source​

Bad Help is not well organized

Feature Help can be searched (but not full-text)

Feature Function / command reference with search (but not full-text) and examples

Source: Although the developers do not state this, the app is based on the open source CAS

Symja

, “inspired by Wolfram Language built-in functions”, and implemented in Java.

Scientific Calculator 300 Plus,

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Graphing calculator plus 84 83,

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Scientific calculator 36 Plus,

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Scientific calculator 30 34,

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Calc 991 Scientific Calculator

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These apps clearly share much code with the Plus 991, even if different developer names are used: Essentially all UI elements other than the keyboard are the same in each of them, and the Symja CAS library is also used (see above).

Thus, it can be expected that they share most of the advantages and disadvantages with the Plus 991.

The main difference seems to be that they are modeled and named after different Casio and TI calculators, and some have a more limited functionality.

Scientific Calculator 300 Plus seems to be essentially the same as the Plus 991.

Graphing calculator plus 84 83 has a significantly different layout, resembling the TI-84 often very closely. It may be better for statistics. Also, it has an alphabetical function catalog.

Below you see the first three.

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