Is "E2" a reserved word?

Is "E2" a reserved word? I cannot declare a variable with this name.

using Toybox.WatchUi as Ui;

class TestingView extends Ui.SimpleDataField {

var E2 = 1.0d;

//! Set the label of the data field here.
function initialize() {
label = "Testing";
}

//! The given info object contains all the current workout
//! information. Calculate a value and return it in this method.
function compute(info) {
// See Activity.Info in the documentation for available information.
return 0.0;
}

}

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BUILD: /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_25.jdk/Contents/Home/lib/tools.jar:/Users/Nick/Software/connectiq-sdk-mac-0.2.4/bin/monkeybrains.jar: com.garmin.monkeybrains.Monkeybrains -a /Users/Nick/Software/connectiq-sdk-mac-0.2.4/bin/api.db -i /Users/Nick/Software/connectiq-sdk-mac-0.2.4/bin/api.debug.xml -o /Users/Nick/Software/workspace/testing/bin/testing.prg -w -z /Users/Nick/Software/workspace/testing/resources/resources.xml -m /Users/Nick/Software/workspace/testing/manifest.xml -u /Users/Nick/Software/connectiq-sdk-mac-0.2.4/bin/devices.xml /Users/Nick/Software/workspace/testing/source/testingView.mc /Users/Nick/Software/workspace/testing/source/OSGridApp.mc
BUILD: ERROR: /Users/Nick/Software/workspace/testing/source/testingView.mc:5: mismatched input 'E2' expecting Id
BUILD: WARNING: The launcher icon 'LauncherIcon' (16x16) is smaller than the specified launcher icon size of the device 'square_watch_sim' (61x43). Padding will be added to the image to center it.
BUILD: Complete