As we've reported, one of the highlights of the H R Harmer auction this week is a classic American stamp error: the 'CIA invert'. But it is just one highlight in a varied event.

The May 12-14 sale contains several mammoth sized consignments both in sheer size and quality. First there is the Raimund G Rueger Never Hinged Estate (less the German related material sold in the March sale at Harmer's sister company Heinrich Koehler which realized multiples of its estimate) with each lot so marked in the catalogue.

The Goldsborough Tristan da Cuhna offers some of the rarest cachets known and many large collection groups whilst the Windsor Classic Great Britain Collection presents specialised First Issues and Mulreadys as well as a major collection balance.

The Pacific Clipper Collection of flight covers, the Kenneth Graham Estate and the Rev. William Kvale collection concentrate on specialised Minnesota.

Hard to see it coming - the baseball stamp sheet with colour error

 Also featured are several unique items including the complete set of Parcel Post large proofs presented to FDR, with a major selection errors as in the newly discovered and certified C10b Lindbergh double impression, a full sheet of the Baseball missing colour error, a 294a Pan American Invert, Canadian Seaway Invert and Double Impression singles and many others.

Let's have a closer look at the Baseball colour error. This is a 1969 6c Baseball stamp set - a top left full pane of 50 - with black (engraving) omitted. Never hinged, it has been folded horizontally between the 5th and 6th rows leaving some perforate separations at the sides.

There is also a light black offset on gum. In very fine-extremely fine condition, it sells against the background of an estimated quantity of 300+ singles known with this being one of the few (if any) full panes remaining.

This makes it a strong investment. It is expected to achieve $ 30,000-40,000 in the auction which takes place in California on May 12-14.