## Saturday, April 27, 2019

### Keep an eye on the delta!

Once you have developed a profile for a coffee you want to precisely duplicate that one in future roasts. Artisan allows to load this successful profile in the background serving as a template for your production roasts. While seeing the delta of your current roast curve and that template helps you to decide if you should slow down or speed up your roast at any moment, especially if zoomed into the graph somewhat. However, often a numeric value expressing this delta is easier to work with. What about adding another LCD to show this delta?

Let's just add one of those magic Virtual Devices which does not connect to any hardware and instead always delivers the value -1 for each of its two channels. Not usefull? Well, the value -1 itself does not tell us much, but we can use a symbolic formula to compute useful values on this channel by combining data from the others.

Here we want to compute the difference between the current bean temperature (BT) to the one of the background profile. Luckily, the current reading of each channel is bound to a variable in the symbolic formula system of Artisan such that we can freely use those values in complex formulas. To find out the name of the variable we quickly open the in-app symbolic formula cheat sheet underneath the help button in the symbolic formula tab for the main device (menu Config >> Device, 3rd tab "Symb ET/BT").

From this table we can see that BT is bound to the variable Y2 and the BT of the background curve to B2. Thus the formula we want to compute is Y2-B2. So we add an extra device under "Extra Devices" (first tab of the Device Assignment dialog), choose "Virtual Device" as type, name the first of its two channels "Delta" and fill this symbolic formula under y1(x). We untick the second LCD and both curves which we do not want to be displayed.

E voilĂ !

How are you using symbolic formulas?