Dc.getSubscreen in an app

Hi,

I'm trying to customise an app to work on semioctagon devices (instinct series, descent g1) but...

When I call dc.getSubscreen() in the onUpdate method, I see:

Error: Symbol Not Found Error
Details: Could not find symbol 'getSubscreen'
Stack: 
  - drawHR() at C:\Work\SVN_GARMIN\App_HIIT_Timer\source\App_HIIT_TimerView.mc:737 0x100055b7 
  - onUpdate() at C:\Work\SVN_GARMIN\App_HIIT_Timer\source\App_HIIT_TimerView.mc:585 0x10006a54 

Surely this should work for device apps in the same way it does for device data fields?

Is there something I'm missing?

G