We all know that Ananda Thero was Buddha's personal attendant -- Wikipedia says,
In the long list of the disciples given in the Anguttara Nikaya (i. xiv.), where each of them is declared to be Prime in some quality, Ānanda is mentioned five times (more often than any other). He was named Prime in conduct, in service to others, and in power of memory. The Buddha sometimes asked Ānanda to substitute for him as teacher and then later stated that he himself would not have presented the teachings in any other way.
So my question is: after Buddha's Nirvana, Ananda Thero became arahant before the The First Council; so what is the position of meditation that Ananda Thero became arahant?