Setting up a proper baseline before investigating - what measurements matter?

I've been reading about how important it is to establish a baseline before you start an investigation, and I want to do this properly. I'm planning to investigate an old church in Oxfordshire that hasn't been used in about fifteen years, and I want to have actual data rather than just wandering about hoping for anomalies.

So far I'm thinking: temperature readings from multiple locations, EMF measurements, light levels, humidity. But I'm not sure what else matters or whether I'm even measuring the right things. I've got a digital thermometer (£25), a basic EMF meter (£45), and I can check light levels on my phone.

Should I be measuring air pressure? Magnetic fields? Electromagnetic frequencies at different ranges? And more how do I document all this in a way that's actually useful when I'm reviewing it later? Any recommendations for apps or logging systems?

Good instinct on the baseline idea. You need: temperature (at least 5 locations spread around), EMF (same as temperature), humidity, light levels, and honestly that's enough to start. Air pressure changes so slowly it's not usually useful unless you're there for days. Document everything in a spreadsheet with timestamp, location code, reading, and notes about external factors.

Use a regular notebook and pen on site rather than relying on your phone. Battery drain during investigation is real and your phone's light will skew your light readings. Photograph the space before you start measuring anything - having visual reference points helps loads when you're reviewing data later. Grid the space out on a map and mark your measurement points clearly.

Should I be measuring air pressure?

Not worth it unless you're there for extended periods. Humidity is more useful actually - sudden humidity spikes can indicate water infiltration or condensation changes that might explain temperature shifts. Get a cheap digital hygrometer (about £15) alongside your thermometer.

For a church specifically, check where heating/cooling systems are, where water pipes run, any air vents. Document all of that in your baseline. Sounds boring but loads of 'paranormal activity' is just explainable based on infrastructure. If you can account for every temperature change through normal building systems, then anything left over is more interesting.

Most important thing: take your baseline measurements multiple times - morning, afternoon, evening, middle of the night if possible. Buildings change throughout the day based on sunlight, temperature shifts, whatever. You need to know what 'normal' looks like before you can identify what's 'abnormal'. Boring but essential groundwork.