There are many features that will assist you in using the ox meter. You should always consider saving previous readings and timestamps; generate various statistics; save readings for more than one person; save readings to a computer for further analysis by you or your doctor; analyze the data; the availability of storage case, and battery, and its easiness of storage.
The accuracy of dosimeter readings are often affected by motion. If your hand shakes, find a model that is more tolerant to hand movements or hold your hand still while taking readings. Fingertip pulse ox meters being operated by inserting your finger into the sensor and then pressing one button, made them easy to operate.