CHAPTER 4 FINAL TESTING
MB23 and MB25 Service Manual
4-3
Ohaus Corporation www.ohaus.com
4.4.2 Repeatability Test
Repeatability is the Standard Deviation of a set of similar readings.
Requirements:
– To perform this test, identical samples must be used for all readings.
– The test sample should be approximately 50 grams.
– Wear gloves when handling the sample.
Before starting a repeatability test, set up the instrument as follows:
TEST PROCEDURE:
1. Zero the instrument.
2. Using a test sample of approximately 50 grams, place the sample on the center of
platform. Record the reading on the worksheet provided.
3. Remove the sample from the platform.
4. Repeat this test starting at Step 1 until you record a total of ten readings
Fill in the worksheet (Table 4-2) with the ten (10) readings
.
TABLE 4-2. REPEATABILITY WORKSHEET
n
Reading
Delta = Reading
– Mean
Delta x Delta
1
2
3
4
5
6
7
8
9
10
n = number of Reading Mean = Sum of readings / 10 Delta = Reading
– Mean
Standard Deviation = Square Root of (sum of (Delta x Delta) / 9)
5. Add the ten readings and divide the total by 10 to find the Mean (average).
6. Mean = (Reading 1 + Reading 2 + Reading 3 + Reading 4 + Reading 5
7. + Reading 6 + Reading 7+ Reading 8 + Reading 9 + Reading 10) / 10
Mean
=________
