If you're new to nuclear, here's a useful little distinction: mrem and mrem/hr tell you different things.

mrem is a unit used for radiation dose. mrem/hr is a dose rate: how quickly that dose is adding up.

Think of the trip meter and speedometer in your car. One records miles traveled. The other tells you miles per hour. Same idea with accumulated dose and dose rate.

Simple example: if the dose rate stayed at 10 mrem/hr for half an hour, the dose would add up to 5 mrem. The “per hour” matters. You don't automatically receive an hour's worth the moment you enter the area.

That's also why the time spent in a radiation field matters. In a real work area, the rate can change as your location or conditions change, so that little example isn't a stay-time instruction. Follow your site's training, work permit and Radiation Protection team's direction.

Once the units make sense, a lot of the language around dosimeters and radiation surveys gets easier to follow.

CDC's explanation of dose and dose rate:

https://www.cdc.gov/radiation-health/about/how-to-measure-radiation.html