  Cardiopulmonary resuscitation (CPR) is one of the most critical emergency
interventions for sudden cardiac arrest. In this paper, a robust sinusoidal
model-fitting method based on a Evolution Strategy inspired algorithm for CPR
quality parameters -- naming chest compression frequency and depth -- as
measured by an inertial measurement unit (IMU) attached to the wrist is
presented. The proposed approach will allow bystanders to improve CPR as part
of a continuous closed-loop support system once integrated into a smartphone or
smartwatch application. By evaluating the model's precision with data recorded
by a training mannequin as reference standard, a variance for the compression
frequency of $\pm 2.22$ compressions per minute (cpm) has been found for the
IMU attached to the wrist. It was found that this previously unconsidered
position and thus, the use of smartwatches is a suitable alternative to the
typical placement of phones in hand for CPR training.
