Can't fin anything closer than Atlas Grotesk you've already found. This /t can't lie to me. But you're right, numerals (/2 is even closer to Helvetica actually). Depending on time period of your sample, could be the original Mercator that Atlas Grotesk is based on: http://typophile.com/node/53257
This /a reminds me of Akkurat.
Quoted from Atlas Grotesk description text

The aesthetic of Atlas was inspired in large part by the sans serifs of the 1950s, specifically Dick Dooijes’s Mercator, released by the Amsterdam Type Foundry in 1957.

Mercator thread:
http://typophile.com/node/53257

Considering the delicate trapping (see the four corners of the "4" for example) this is probably a font made in the late 20th century.

hhp

It sure looks like Mercator including the numerals. If that’s printed from digital data it must be Laurenz Brunner’s digital version mentioned in the above thread.

Mercator does make sense - the Amsterdam Foundry was big on trapping.

hhp

Thanks for all these interesting informations. – Isn't that lowercase »a« of Mercator just perfect!
Regarding the layout it reminds of Laurenz Brunner's handwriting too.

Corina Neuenschwander and Simone Koller designed this – including poster, invite etc. for an exhibition at Helmhaus Zurich, on show in spring 2013. The font is indeed Laurenz Brunner's version of Mercator.
There's also this book, worth checking out, although in german only. http://