Oakton 1413 TDS Solution is made specifically for Oakton® meters and testers. This Oakton® Conductivity/TDS calibration solution has been fully cross-checked using different test methods and comes premixed. This means the solution is ready to use the day it arrives! NIST traceable materials. Solutions are proven to obtain ±1% accuracy at 25°C. Obtain the most precise readings with Oakton products. 500 mL bottle.