public Callable<Double> getPositionCallable() {
   if (lastImageNumberStreamIndexer == null) {
     logger.info("Creating lastImageNumberStreamIndexer");
     timeSeriesCollection =
         new ZebraCaptureInputStreamCollection(
             zebra.getNumberOfPointsCapturedPV(), zebra.getEnc1AvalPV());
     lastImageNumberStreamIndexer = new PositionStreamIndexer<Double>(timeSeriesCollection);
   }
   numPosCallableReturned++;
   return lastImageNumberStreamIndexer.getNamedPositionCallable(zSM.getName(), 1);
 }