I used to draw lines on the full bag with a red permanent marker. I used to hang the bag about four feet off the floor, but sat on the floor when giving Bob fluids. It was the only way I could see the "marks" from that angle.
Thanks. I can see the lines/numbers but the fluid level is elusive. It's at about 2 but need a 2nd set of hands while giving fluids to manage the bag. I'm going to put something dark behind it as someone has mentioned so there's some contrast.