If you, unlike me, dive Nitrox on a regular basis then you probably have a Nitrox analyzer. I don’t own one and one of the instructors I dive with is selling their Analox Nitrox Analyzer O2EII. Analox is one of the more popular brands. The O2EII is a small portable Nitrox Analyzer perfect for keeping in the dive bag. It doesn’t offer much leeway in terms of other mixes (trimix) but it’s super portable and “only” $300.