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Hey! DA scores are specific to the root domain, we are not taking into account a subdomain.  So even if you search a subdomain that doesn't exist (ffff.blog.ir), DA score is still only relevant to the root domain (blog.ir) which does exist. Page Authority on the other hand is specific to the exact page you are searching, so it makes sense that mihanblog.com and hfilm.mihanblog.com would have different page authority scores are they are separate pages. Hope that helps, let me know if you have further questions.