pH,EC

i dont know what you consider cheap, but there are multiple models for 30-50 euro and that aint cheap for a ph/tds-meter, they work well and like u said are recalibratalble.

The ph meter I have works very well for a year now, but I'm thinking about buying another to see how far its calibration has gone off. It's the Yinmik YK-P01. and has good reviews. It's only 11 dollars. the TDS meter I bought however I did not skimp on its the Blue Labs truncheon commercial and that was 120. It does not give precise readings but is very reliable and used widely in agriculture but if you are doing a lot of bottle feeds you are going to need something that measures more precicly. for my organic style of growing I only need a ballpark on my tds reedings

I don’t recommend buying cheap PH and TDS meters. Spend a bit of money and get tools that will be reliable. I have an Apera PH60 for measuring PH and an HM digital TDS meter. Buy cheap and you’ll have to replace them when you realize how crappy the tool is. These are tools that you’re relying on to be accurate. Also consider you’ll have to invest in the calibration solutions as well.

I find them much easier to use and more accurate than the drops and straps.