Birdnet .. that is a very good lobang.
Anyway, I am aware of where to get the TDS calibration solution at a much inexpensive price for USD $3.50 for a set of 3 pkts. Damn it .. I paid USD $5.85!
If any bros intend to buy the TDS meter from Birdnet's lobang, let me know so that I can "tobang" something to share out the shipping charges.