Shares of banking giant Barclays were performing well on Wednesday morning, helped by an upgrade from Investec which recommends investors to build positions following the stock's recent underperformance."An interesting day for an upgrade?...but any further sell-off today offers a clear opportunity," said analyst Ian Gordon. Before today's open, the stock had dropped 20% since March 2nd. Gordon notes that Barclays is now trading at just 0.5 times 2011 tangible net asset value (tNAV).Nevertheless, the broker's sceptical medium-term view on the company is unchanged - "profitable, defensively positioned but low returns". Investec's 2013 return on equity [forecast] is 7.6% compared with the company's own 13% target.Ahead of the first quarter update on April 26th, the broker highlights the 15% appreciation (during the three-month period) of Blackrock, which is 19.7%-owned by Barclays. This alone is worth 5p on tNAV.For the full-year, Investec expects Barclays Capital to generate £11.1bn in revenue, ahead of consensus estimates of £10.9bn and last year's £10.3bn.By 10:55, shares were up 4.26% at 215.08p.BC