Accuracy of formula preparation equipment for liquid measurement

Modular specialist feeds may consist of a number of individual liquid ingredients. Accurate feed preparation is dependent on competent liquid measurement. We investigate the accuracy of two measuring jugs (one retail mix-and-measure; and one produced to laboratory standards); and the influence of volume and technique on accuracy.

20 health professionals aged 18-60 y (mean: 46 y) measured 3 different volumes of water with each of two measuring jugs. For each volume with each jug, 2 measurements in randomised order were made: 1) eye-level with the jug, and 2) standing upright (total of 12 measurements). Measured quantities were weighed and the difference between measured and target volumes calculated.

The laboratory jug was more accurate (mean difference 9.3 ml, range - 30.5 to 57.5 ml, std error mean 1.59) than the retail jug (mean difference - 17.7 ml, range - 92.0 to 48.5 ml, std error mean 1.59). Accuracy improved with increased volume (450 ml: mean difference - 9.4 ml, range - 75.5 to 49.5 ml, std error mean 1.95; and 810 ml: mean difference - 0.7 ml; range - 92.0 to 43.0 ml, std error mean 1.95).

Accurate measurement of liquid ingredients is difficult to achieve even for trained professionals. The cumulative effect of many different liquid measurement errors (inappropriate jug type, inaccurate volume measured and poor technique) may lead to clinically important errors in the preparation of modular specialist feeds.