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Tread Lite Gear says:
Ideal for the things you want to keep handy during the day. Rear has a strap loop and an anchor loop complete with slick slip to attach on your pack strap. Just remove the pack strap from the adjuster buckle, slide the pocket on and re-thread the pack strap.
Like all manufacturers, Tread Lite Gear recommend a ziplock bag for moisture sensitive items such as cameras and other electronics.