What Does it Really Mean?

Fifty-eight years ago it meant just what it says. Today these words can still be found in many technical specification sheets and literature, but today the phrase can be misleading, erroneous and meaningless because many makers have copied this cup and their efflux time in seconds can greatly differ from one make cup to another make cup, from one production run to another, as well as from one cup to another in the same lot. Differences of over 50% have been recorded.

The Zahn Viscosity Cup was originally patented by E.A. Zahn of the General Electric Company. This U.S.Patent No. 2,141,329, dated Dec. 27, 1938, was assigned to G.E.. General Electric no longer manufactures Zahn Cups.

Some original specifications were based on the early G.E. Zahn Cups. Unfortunately, such cups were not calibrated which often resulted in variations of efflux time in seconds from cup to cup. We make two calibrated Zahn type cups that do differ in efflux time in seconds in order to meet both past and present specification requirments. These two cups are the GARDCO S90/Zahn Signature Dip Cups and GARDCO EZ Zahn (ASTM) Dip Cups.

GARDCO S90/Zahn Signature Dip Cups are designed to meet the earlier specifications. Be sure to update your specification sheets and literature to include the type of Zahn cup (EZ or S90/Zahn Signature), the cup # and the efflux time in seconds. Only use CALIBRATED cups with a GARDCO (Paul N. Gardner Co., Inc.) nameplate.


1. You can convert S90/Zahn Signature Dip Cup readings to ASTM D 4212 readings using the EZ to S90/Zahn Signature Seconds Conversion Charts by GARDCO. This will allow you to maintain the records you have established with your S90/Zahn Signature Dip Cups, and also enable you to invert to ASTM D 4212 readings if necessary, even though the cup Constants and Formulas for the S90/Zahn Signature Dip Cups differ from ASTM Specification D 4212. Sets of graphs with flow curves detailing these differences are available on request.

2. GARDCO Cups give reliable, credible, accurate readings.

3. EZ Cups are calibrated to within 3% tolerance.

4. S90/Zahn Signature Dip Cups are calibrated within 5% tolerance.

5. All GARDCO Cups are calibrated and furnished with a set of Calibration Charts to convert seconds efflux time to viscosity in Centistokes.

6. A wall size "Viscosity Cup Equivalent Chart" allows you to convert efflux times in seconds to viscosity in Centistokes for all 45 cups made and calibrated.

7. All GARDCO cups are calibrated with standard liquids traceable to the National Institute of Standards and Technology.

8. Both GARDCO EZ & GARDCO S90/Zahn Signature dip cups qualify for Calibration Certification under ANSI/NCSL Z540-1 or MIL-STD-45662A as applicable.

9. Oils used to standardize GARDCO Cups are produced in accordance with ISO 9002.

10. Take advantage of the 20% trade-in allowance on your old Zahn Type cup for purchase of a new EZ cup. (Dealers Excluded).