UKOM is set to launch in January with a panel of 35,000 users selected by Nielsen to be representative of the general UK population.
Panellists will be profiled by: gender and age from 2+; region/geo demographics; occupation and income; social grade; main shopper; and whether they are in the market for cars, houses and other products.
Data on video will be introduced following the launch of UKOM in January, as part of UKOM's intention to focus on the different activities, such as instant messaging, that consumers spend time on while online.
Video data will include demographics, duration, stream count and attribution.
The focus on time spent was criticised by a delegate from Worth Digital, who asked what time spent actually means and why UKOM doesn't measure the behavioural changes resulting from that time spent.
However, IAB chief executive Guy Phillipson, who co-presented the UKOM session with Ainsworth, emphasised the system's purpose was to give advertisers data comparable to other media currencies such as Barb and Rajar to allow them to better plan online campaigns in terms of demographics and reach.
Ainsworth said: "The big issue for the internet is starting to think about planning in a brand way. That is what UKOM is addressing."
She also defended the focus on time spent, saying: "Page impressions continue to be a very important volume metric but the reality is that audiences are using the internet in different ways and time spent is becoming very important."
Rob Salmon from Molson Coors and a member of the ISBA digital working group, applauded the introduction of the system but questioned the assertion that UKOM would be able to focus on the long tail of niche websites, down to those with 35,000 unique users.
Salmon said: "With this new system, if nobody on the panel visits a website presumably it won't be on the data."
Ainsworth agreed that would be correct, and added the system "would show very clearly where the projections are based on a very small number of panellists".
The UK Online Measurement Company is funded by the IAB and the Association of Online Publishers. Its creation followed the abortion of a previous plan to create a more generously funded system also having the financial support of the IPA and ISBA.
The tender to deliver a measurement system to UKOM was contested by Nielsen and ComScore.
The winner, Nielsen, proposed a panel-based system combining data from 31,000 consumers using the web at home and 4,000 using it at work and providing both reach and frequency metrics.
ComScore has said it will roll out its system, focused on recording actual user sessions, as an alternative to UKOM.