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## Plotting values relative to the first time state

Plotting a variable relative to its initial values can be important for understanding how the variable has changed over time. The conn_cmfe expression is also used to plot values from one time state relative to the values at the current time state. Consider the following expression:

<mesh/ireg> - conn_cmfe(</usr/local/visit/data/dbA00.pdb[0]i:mesh/ireg>, mesh)

Figure 18

The above expression subtracts the value of mesh/ireg at time state zero from the value of mesh/ireg at the current time state. The interesting feature about the above expression is its use of the expression language's [] operator for specifying a database time state. The expression uses "[0]i", which means use time state zero because the "i" suffix indicates that the number inside of the square brackets is to be used as an absolute time state index. As you change the time slider, the values for the current time state will change but the part of the expression using conn_cmfe, which in this case uses the first database time state, will not change. This allows you to create expressions that compare the current time state to a fixed time state. You can, of course, substitute different time state indices into the conn_cmfe expression so you don't have to always compare the current time state to time state zero.