# Is a ndc less than five is also acceptable?

#### jelly1921

##### Quite Involved in Discussions
on page 129 of MSA 4th:
GRR = 0.302 (STD. DEV.) 27.9 % TOTAL VARIATION
and
ndc = 4 (what I calculated is 5.0609 )
why the book says Measurement System is acceptable for Process Control and Analysis when ndc is less than 5? mistyped?

Jelly

#### Stijloor

Super Moderator
A Quick Bump!

Can someone help?

Thank you very much!

B

#### Bezerra

The ndc must be greater than 4. Otherwise you will not have significant values to accept the study. Also you must pay attention how to calculate the ndc it will depend on how you get the TV value.
Hope it was helpful. If need something more just say.

Stay well.

#### Miner

##### Forum Moderator
on page 129 of MSA 4th:
GRR = 0.302 (STD. DEV.) 27.9 % TOTAL VARIATION
and
ndc = 4 (what I calculated is 5.0609 )
why the book says Measurement System is acceptable for Process Control and Analysis when ndc is less than 5? mistyped?

Jelly

Page 129 is indeed a mistype. The calculation at the top of page 128 shows that the ndc ~ 5.

#### bobdoering

##### Stop X-bar/R Madness!!
Trusted Information Resource
See page 47 of the AIAG MSA 4th edition for when ndc less than 5 is acceptable. Although not indicated in the AIAG book, you should have an ndc of at least 10 for a gage used for SPC. Anything less generates "chunky" data, and is virtually useless.

#### jelly1921

##### Quite Involved in Discussions
See page 47 of the AIAG MSA 4th edition for when ndc less than 5 is acceptable. Although not indicated in the AIAG book, you should have an ndc of at least 10 for a gage used for SPC. Anything less generates "chunky" data, and is virtually useless.

Where does this criteria come from? A best practice?

One more question:
if ndc = 45 or more, it may be a good news for appraisers, but a bad one for boss. Therefore, for cost saving, we'd better change the gage to reduce the ndc.
Is there such criteria or threshold? or in other words, when should we change the gage, if ndc is larger than certain number ?

Thanks

Jelly

Last edited:
A

Hi guys
i think my prob is same like others, which ndc is less than 5.
I m using anova method to report my GRR result to my customer.
unfortunately ndc value is 1.
Could someone help me please..
Data attached.

#### Attachments

• NDC again.xlsx
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