@tf.function
def exceeds_threshold_fn(reading,threshold):#on-device processing    
    return tf.to_float(reading > threshold)

@tff.federated_computation
def get_fraction_over_threshold(readings, threshold):    
return tff.federated_mean( #collective operations                           
       tff.federated_map( #collective communication                     
            tff.tf_computation(exceeds_threshold_fn),                       
            [readings, tff.federated_broadcast(threshold)]))