The WhiBal SLR is a Spring Loaded Retractor that allows you to keep the WhiBal reference card close at hand by attaching the SLR to your belt, or shooting jacket, or shirt pocket; or any other appropriate attachment point. Just pull the WhiBal for use, and the SLR will automatically retract when finished. The WhiBal SLR provides the proper combination of long life, appropriate pull strength, and ease of use.