The main job of finding out is to draw waveforms parameter values. The user opens a set of graphs, sets at a time, and the program reading the parameter values and for each of the intervals (X-axis points) plotted on the graph parameter values.
Notatka: Example: if you watch only one parameter, we are on the screen year and in addition lined up at the beginning of 2012, is to draw a graph of the program browsing learns what the average  parameter value for month of January 2012, February 2012, March 2012, etc., then the thus obtained values are presented as a graph parameter.
For parameters collected by the system directly SZARP (eg outside temperature), it's simple, the program browsing pulls the corresponding values from the database, asking the database - what is the average outside temperature in January 2012, February 2012, March 2012, etc., and if we are to screen a month it will ask what is the average temperature in the next days. So it is with definable parameters - the program browsing asks what is the average value of the parameter for the month of January, February, March, etc, has only been in this case does not reach the value directly into the database but uses a formula parameter definable to get the desired value.
And whence the name of definable parameters LUA? Definable parameters LUA are called so because their record is used scripting language LUA. It is quite a popular language with a syntax based on C / Pascal, a person familiar with the basics of seeing the example code in LUA certainly quickly find familiar structures.