Hemorrhage is the leading cause of preventable battlefield deaths prompting the utilization of walking blood banks and fresh whole blood (FWB) in the military setting which has now become fluid of choice for trauma resuscitation of the military casualty. Each branch has initiated its own system for collection of fresh whole blood (FWB), including but not limited to the Army Special Operations ROLO, Naval Special Warfare SOLO, and Marine Corps Valkyrie Emergency Whole Blood programs. While in the field, these programs bypass the clunky, time intensive blood bank processes and directly draw and transfuse blood from donor to patient while coordinating damage control resuscitation (DCR). As part of this, they utilize standardized austere methods of estimation to determine blood bag volume prior to terminating the draw to target the Joint Trauma System (JTS) standard of 585g. Inaccurate volumes do carry risk, with underfilled bags risking inducing hypocalcemia in the recipient and overfilled bags increasing the risk of thromboembolic complications. This is due to the citrate based anticoagulant within the bag, designed to prevent clotting and fix calcium for a 585g volume, being insufficient or excessive for volumes outside of tolerances (+/- 10% per the AABB and FDA). The recent study looking at volume methods, Valkyrie Volume Validation (V3) Study, Carlton et al. 2023, showed of these commonly used methods, operator prefer utilized the Operator Gestalt (OG) method, a visual estimation method relying on the operator to identify a full bag when the bag “dimples” and has a visible “air-fluid level”. While both the V3 study and the 2017 Meledeo study reviewing the ROLO methods both demonstrated upwards of nearly 70% accuracy with this method, that still left nearly one third of bags outside of the acceptable volume range. The goal of this study is to investigate if the addition of standardized markings on the bags can further reduce the error of the preferred gestalt method. We will determine where appropriate markings on the bag need to be made and attempt to create a ruler for operators to pre-mark bags.. The study will be conducted in two parts: First a bench trial and then, a live field trial. This portion of the study will solely focus on the bench portion. The first part we will fill 20 blood bags with 50cc increments of water, marking the water line after each 100cc added. The bag will be free hanging the entire time to avoid any possible confounding secondary to water displacement. Lines will be marked up to 450cc. After this the bags will be drained and the markings will be measured in distance from the bottom of the bag. The lines will then be transferred to a paper where the distance will be measured. The average will be taken across the papers to develop a ruler. This ruler will be used to mark volumetric marking atl 450cc. These bags will then be weighed to approximate volume and be draining into a secondary collecting system to assess for accuracy. Results of this study are intended to improve techniques for Department of Defense wide prehospital blood program accuracy.