Many of the themes and some of the objects staple to our story here at the Board of Longitude project are ones that have a much wider currency than academic history. This was demonstrated when one of the team working on the NMM's planned exhibition on longitude spotted the online design description of the New Zealand passport.

Navigation, travel and exploration are, of course, entirely appropriate themes for passport imagery (although the 2010 design for the UK passport is distinctly insular), but in the New Zealand case they are also very closely associated with national identity. As the description explains, the designs were to show "our evolution from a place of discovery, to a place of destination".

"The journey begins at sea, with New Zealand below the horizon, representing the leap into the unknown made by early Polynesian explorers who speculated on the existence of land to the south based on the patterns of migratory birds. Travelling towards New Zealand, the land appears and the viewpoint moves closer. As the coastline is reached, the view moves towards a harbour, travels up a river and into the mountains, representing the waves of exploration that penetrated New Zealand’s hinterlands.

Finally the journey ‘launches’ from the summit of Aoraki Mount Cook, representing the modern aerial explorations and journeys made today. In addition, a progressive journey is also made from north to south to reflect the general geographic pattern of exploration and settlement."

We are taken through the design, page by page. It reflects both western and native traditions and uses motifs that show a range of navigational techniques that can be used - cloud, ocean and land patterns, the constellations of the southern hemisphere and maps. Over all we are presented with a progressive journey and story, moving from "traditional to contemporary, and natural to technological".

Even if this might seem a little linear, it is nice to see mention of planisphere, compass, the use of a canoe as a compass, astrolabe, sundial, marine clock, sextant, radar and GPS - and of course, Cook and the Endeavour. There are, though, a couple of points to make a specialist raise an eyebrow. The "astrolabe and chart" on pp. 21-22 certainly wasn't used for "determining local time using local longitude and vice-versa", for example, but for me the greatest curiosity is the choice of illustration for pp. 30-31.

That it is devoted to Harrison and the development of the marine timekeeper is understandable, and, correctly, the blurb tells us that "after 40 years of work, in 1764 [Harrison] proved that a clock could be used to locate a ship's position at sea with extraordinary accuracy". What is odd, though is that, despite the accuracy of the date, the illustration is of the earlier H1 and the blurb goes on to state that after 1764, "Further developments led to the H4 clock", when it was H4 that had been trialled.

The level of accuracy and detail is again revealed by saying that it was H4 that "was copied by Larcum Kendall and used by Cook on his voyages". But given that H4 was the timekeeper that gained the largest reward, and that it was Kendall's K1 that was actually used by Cook and made it to New Zealand, why the prominence given to H1?

I haven't seen the actual passport, but I assume that none of this explanation is there (or that people spend much time looking at or making sense of the pictures). It is simply an illustration and perhaps H1 has benefits in this context over H4, in terms of producing a complex design that it hard to forge. Yet I think it is the case that that the early clock has become much more iconic than the much-rewarded watch. There is, for example, an H1 iPhone app available but not an H4 one, and it is H1 that is pictured on signage outside the Royal Observatory.

It speaks, I think, to the engaging nature of this clock - its unusual appearance, its moving parts, its openness, its sense of a unique mind working on a unique solution to an intractable problem. While visitors are certainly struck by, and often comment on, the sudden change in the sequence from the large H1, H2, and H3 to the smaller and entirely different H4, I think that on its own it would much more likely be looked over. After all, it simply looks like a big watch, and its movement is usually hidden.

For the purposes of a designer or illustrator, how much more likely would it be to choose the curious object that might make people stop and ask a question over the watch? And even if you chose H4, who would know whether you had in fact chosen K1? Having two such unique and important objects that nevertheless look almost exactly the same is, it turns out, rather problematic. It is, likewise, interesting to reflect on how Harrison would be considered today had his earlier marine timekeepers not survived just long enough to be rescued and restored by Rupert Gould.