It is an IME that facilitates inputting mathematical expressions.

Keys are divided into different key-groups.  The Criteri-R key-group targets the Criteri-R app.  The User key-group allows users to  define their desired key texts like macros.  Alphabets and General punctuations and symbols are added for normal inputs.

Besides the common math input keys, on the keyboard there are a number of mutable keys whose contents can be changed to map to any keys in the selected key-group.  Users can define as many keys as they need in the User key-group.  In this way, Math Keyboard can be used to serve Criteri-R as well as other apps, e.g. Excel, WolframAlpha, etc.

Superscripts, subscripts and more characters are available through in-app purchase.

In analog circuit design, calculating component values is not straight-forward because they are quantized into what known as 'E-series'.  Criteri-R is a tool that helps finding out such component values that comply to various user criteria.

Instead of equations, inequality pairs are input as criteria for determining whether the mathematical outcome of certain quantities based on a set of component values be acceptable and hence a solution found.  Every combination of component values in the E-series is tested to see if it is a solution.  Solving processes are accelerated with proprietary optimizations.  Users may limit the criteria to control the physical tolerances as best as they wish.

In Criteri-R, you define named components for use in mathematical expressions.  You define criteria in mathematical terms for controlling the acceptance of your physical quantity values.  You may also define functions to help simplifying mathematical expressions.

In case some components possess non-zero tolerance, each (primary) combination of component values further evolves into secondary combinations of values due to the 2 toleranced values of every component.  Only if all these secondary combinations lead to results fulfilling all inequalities, will that primary combination be deemed a solution.  This feature is termed Extreme Values Analysis.

Criteri-R is free, but with a limited number of items (components/functions/criteria) and component value combinations.  You may increase the number of these items, as well as enhancing other features, through in-app purchasing.