Note: CPI (Contents Power Index) is an integrated index that calculates news subscription rankings, direct search rankings, and social media buzz rankings (from SNS & etc.); and measures from 125 programs amid the genres of dramas, entertainment (i.e. variety), music, and infotainment that are on the 3 terrestrial broadcasts (SBS, MBC, KBS) and 6 CJ E&M channels.
The Content Power Index, developed by CJ E&M and Nielsen Korea, is a model used to measure the influence of broadcast contents.
Let’s tag #Manhole or #맨홀 when you leave a comment on Twitter, Instagram, etc.
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Nro 7 KBS2 Manhole Drama
JYJ3 
from https://www.soompi.com/2017/08/27/age-youth-2-tops-list-buzzworthy-tv-dramas/
Manhole is #8
(Good Data corporation found these results by gathering data surrounding 36 broadcast dramas starting from August 21 to August 27, analyzing netizen responses through online news, blogs, community social media posts, and videos.)
I think Manhole is consistent in the top 10, no wonder it still has the advertisers/commercial sponsorship despite the much hyped low tv rating.
This statistical ranking has broader coverage than tv rating/
GB Nielsen (South Korea)Panel
– Metropolitan area measurement includes 5 major cities and 5 medium-sized cities with 2050 household panels.
– Metropolitan area households include Seoul 550 and Gyunggi-Incheon.
– 4 major city households include Busan 250, Daegu 200, Gwangju 160 and Daejeon 160.
-5 medium-sized city households include a total of 290 in Gumi, Masan, Jeonju, Cheongju and chuncheon.
-The TV Establishment Survey is conducted 3 times a year to ensure that the selection of panel households is reflective and the TV ratings data remains representative.
-Up to 25% of panel households are replaced each year.
So the ratings for Manhole from ep 1-16 are basically from the same household panels, before I thought they do the sampling every episode.