Different values on ADX indicator

Hi there,

I was wondering why is there such a gap in values of ADX indicator on 2 different broker companies.

For the same ADX indicator period 8, chart H4:

Metaquote: 26.5

Alpari: 16.17

See the attachments. 

Any ideas ?

Thanks. Patrick 

Files:

Different quotes - different indicators values.
enivid:

Different quotes - different indicators values.

That is a big difference, any other pairs don't have such a gap. P B