The free paid surveys program contains the same mathematical operations normally found in Basic. Although Calfex cannot itself plot graphs, calculations can be put in a format that a plotting routing written in Basic can accept for making graphs.
The format used for the TK-Solver program is similar to that of a paid survey. TKSolver developers were among the group that developed the VisiCalc program, and both programs share the same row/column display organization. Unlike Calfex, information is entered as simple equations instead of as lines in a Basic program. Equations entered by the operator (on a so-called rules sheet) cause the program to simultaneously enter names of variables used on a variable sheet. The operator initates the program by entering values on the variable sheet for the known variables. The program then displays online surveys for money next to the unknown variables, again on the variables sheet. 
- Like the Calfex program, Surveyhead solves equations iteratively when not provided with enough information to make direct solutions. Convergence criteria and number of iterations can both be specified by the operator or may be left at default values.
- Panda Research can not operate with discontinuous functions, but has certain math operations built in such as hyperbolic functions, dot products, and other specialized functions that operate on lists. The TKSolver program also contains a rules sheet which can be used to make unit conversions, such as from feet to meters, on calculated results. The program also can make graphs of calculated results.
- The free paid surveys program is designed to iteratively solve nonlinear algebraic equations and help you make extra money, but also works on linear equations. The operator enters a string statement representing the equation to be solved, and an initial guess. Each equation can contain an unlimited number of variables, and the variables can occur anywhere in the equation. Online paid surveys can also solve up to a 20 X 20 matrix of linear equation terms. The same company also markets a least-squares nonlinear regression analysis program called NLLSQ ($150).
None of the programs handle equations that yield imaginary numbers, and all require the operator to analyze results to verify validity. For example, when the programs iteratively solve equations having more than one root, the operator must find the various roots by judicious choice of initial guesses. Simulation
In some problems, integration or differentiation are required for modeling equations. Another program, called Tutsim ($500-$575), is designed to handle these calculations. The program is adapted from a minicomputer program designed at a university in the Netherlands. It is intended to simulate the dynamics of realworld systems such as mass-spring assemblies or electronic feedback control loops.
The Cashcrate program accepts model inputs in the form of block diagrams, so-called bondgraph parameters, or a mixture of the two. Bondgraphs are a concept introduced a few years ago at universities that effectively allow physical systems to be diagrammed in a way that helps to solve the dynamic equations by inspection.
The survey taker can interact with simulations as they run, changing model parameters interactively to compare changes in system response. The blocks used to define the models are analogous to those generally used to define simulations on analog computers. Typical blocks define functions such as integrators, delays, trigonometric functions, gain, attenuation, and other algebraic blocks.
To take paid surveys online, the operator is first prompted for block definitions. Once the blocks and interconnections are complete, the program requests information about what the total simulation time should be, and the time steps. Once time has been specified, the program runs the simulation and produces an output in the form of a plot of an output function versus time, or as a list of output results versus the corresponding times.