//..TB TODO timer by DO so can swap implementations
 public MeditationTimerViewModel()
 {
     _timer = new Timer(DecreaseTime, null, 1000, 1000);
     _model = new MeditationSession(new TimeSpan(0, 20, 0));
 }
 //..TB TODO timer by DO so can swap implementations
 public MeditationTimerViewModel(IAudioService audioService)
 {
     _timer        = new Timer(DecreaseTime, null, 1000, 1000);
     _model        = new MeditationSession(new TimeSpan(0, 20, 0));
     _audioService = audioService;
 }