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Short answer: the TP50 is what you want on a shelf in a room, a greenhouse or a store cupboard, showing conditions continuously with no app. The 605i is what you want in a tool bag, for taking measurements in places a shelf instrument cannot go.
What Each Listing States
| Item | TempPro TP50 | Testo 605i |
|---|---|---|
| Measures | Temperature and relative humidity | Temperature and relative humidity |
| Stated accuracy | Plus or minus 2 to 3 percent RH, plus or minus 1 F | Not given in the bullets |
| Update interval | Every 10 seconds | Live feed to the app |
| Derived values | Comfort indicator: dry, comfort, wet | Dew point and wet bulb, calculated automatically |
| Records | High and low temperature and humidity | Through the app |
| Probe | Sensor in the body | Compact head bendable to 90 degrees |
| Display | Own screen | Phone or tablet |
Continuous Presence Beats Occasional Precision
For most humidity problems, the valuable information is not one precise reading but a record of what a room does over days. A cupboard that sits at 70 percent all winter, a greenhouse that swings from 40 to 95 percent between noon and midnight, a bedroom that only gets damp when the door is shut: those patterns come from an instrument that lives in the room. The TP50 retaining high and low values is exactly the feature that makes a cheap hygrometer useful, because you learn what happened while you were not watching.
The Comfort Indicator Earns Its Place
A dry, comfort and wet icon sounds like packaging fluff, and in a household it is the most used feature on the device. Most people do not know what 55 percent relative humidity implies, and they do know what an icon means. If the point of putting an instrument in a living room is to change behaviour, a readout anybody can interpret does that better than a precise number nobody understands.
What the Professional Instrument Adds
Three things: reach, derived values and portability. The bendable probe measures in ducts and voids. The automatic dew point and wet bulb answer condensation and psychrometric questions without a chart. And it is a tool that travels, taking measurements at many locations in a day rather than one location over many days. For a trade diagnosing a damp complaint, those are the capabilities that matter, and no shelf hygrometer substitutes.
Many Jobs Need Both
A damp investigation typically starts with a professional instrument taking spot readings and surface temperatures, and ends with a cheap logger or hygrometer left in the room for a fortnight to see what actually happens. The two are complementary rather than alternatives, and the inexpensive one often produces the evidence that settles the argument.
Who Buys Which
- Home, greenhouse, storage, instrument case or wine store: TP50.
- HVAC, building diagnostics, duct measurement: 605i.
- Condensation and mould investigation: 605i for the diagnosis, TP50 left behind for the evidence.
- Several rooms at once: several TP50 units cost less than one professional probe.
How We Research
All figures come from the manufacturer listings. We did not run laboratory tests and publish no measurements of our own. Ranking in the digital hygrometer roundup.
Recommended Tools
Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.
Frequently Asked Questions
What accuracy does the TP50 state?
The listing states plus or minus 2 to 3 percent relative humidity and plus or minus 1 F, with readings updated every 10 seconds and high and low records retained.
Can the TP50 be used in a duct?
No. It is a room instrument with its sensor in the body. Duct measurement needs a probe, which is what the 605i provides with its 90 degree bendable head.
Does the TP50 need an app?
No. It displays temperature, humidity and a comfort indicator on its own screen, which is the main reason to choose it for a room, a greenhouse or a storage area.
Which is better value?
They are not competing on value. The TP50 monitors one place continuously for very little. The 605i takes professional measurements anywhere, calculates dew point and logs to a phone.
Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.
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