Air bubbles in the sample will cause inaccurate readings. The float must be kept free from the wall of the hydrometer. Both are determined in field testing to be more accurate and reliable that the typical hydrometer. The difference between using a refractometer versus using a test strip is the desired result. Emissions control is impossible without the proper concentration.
Catalytic converters are fickle at best.
The bottom line is the cost of not measuring properly is in the maintenance costs and poorer performance of the vehicles. Specifications are subject to change without notice. We reserve the right to correct errors without warranty or obligation. All trademarks are the property of their respective owners.