Less than a month after a Microsoft PR executive dismissed Apple's Pages, Numbers and Keynote productivity software as "watered down imitation apps," the company has erected giant billboards depicting its own Excel failing to add seven numbers correctly on a Surface tablet.

The advertisements (including the one above at Market Street at Sanchez in San Francisco) depict a Surface with a bright blue keyboard displaying an Excel spreadsheet for calculating vacation expenses and presenting them as a pie chart.

The device also displays a photo of Hawaii in a separate window at the same time. "This is not just a laptop," the ad announces, "this is the new Surface. One device for everything in your life." "Helping folks kill time on a tablet is relatively easy. But helping people be productive on a tablet is a little trickier" - Frank Shaw, Microsoft

The ad was presumably approved by Microsoft's Corporate Vice President of Communications Frank Shaw, who last month penned a scathing dismissal of Apple's iWork productivity apps for Macs, iCloud and iOS devices after the company announced it would make new versions of its software available for free with new hardware sales.

In his scoffing public tirade, Shaw stated, "Surface and Surface 2 both include Office, the world's most popular, most powerful productivity software for free," adding that "Apple's decision to build the price of their less popular and less powerful iWork into their tablets [is] not a very big (or very good) deal."

Shaw added, "let's be clear - helping folks kill time on a tablet is relatively easy. But helping people be productive on a tablet is a little trickier," and ended with a jab at the "struggling, lightweight productivity apps" Apple is now offering at no additional cost.

Enhance!

Despite the incredible "power" of Office's productivity, Microsoft's own depiction of its software running on its hybrid tablet results in a $500 error. Charged with adding up just seven rows of numbers, Microsoft Excel running on the Surface comes up with a total of $9,000, as can be seen in the zoomed in detail below.

The correct sum for the numbers is $9,500, which Apple's Numbers app has no problem calculating on either an iPhone, a Macintosh, or even the beta version of iWork for iCloud accessible via a web browser. Despite lacking some features, such as chart editing or 3D depictions, the browser accessible Numbers can still add correctly.

The only explanation for Excel's big billboard bug blunder is that perhaps Office is stuck writing off most of the cost of the Surface in its calculations, after Microsoft was similarly forced to erase $900,000,000 of its earnings after Surface tablets failed to sell last year.