Hand-held TDS meter: Faded numbers - Fading numbers usually means that the battery needs to be replaced, this is a simple fix. Jumbling Readings - If the probe hasn't had a chance to settle or if the probe has moved, then your readings can bounce up and down before giving an accurate measurement. If it never settles, try redoing the test using a fresh sample. Inaccurate Readings - This could mean that you need to calibrate the meter using some calibration solution. It could also mean that you need to replace the battery. If you try the battery first and still do not get a change, use the solution. If neither works, then you may need a replacement meter. The cheap TDS meters cannot be calibrated. Dual TDS Meter: This is about the same as a hand-held. The only difference is the probe. If you have readings that jump around, remove the probes from the fittings (with the water off) and reset them. The same process applies to using the calibration solution. Some of the Dual TDS meters came with LED backlighting, the newer one does not. TDS Alarm (Extreme Typhoon III): The alarm is a different matter than the TDS meters. It only has one light; a red one. This is the only light you have to worry about. If the TDS coming out of the DI is15 PPM, this red light will come on. To test this, simply remove the probe from the fitting and put it in a glass of tap water. If it does not come on, then simply replace the batteries.