Blimey, second question I have for the TML inside a year.

Shock!
Horror!
Cats and dogs living together in harmony!
Solomani Confederation peacefully reintegrated into Third Imperium!

Why does the SPA-special exchange rate (GT: Starports, p67) seem to be
applied twice when determining the amount of effort required to actually
build a port of Class II/D or higher (p63)?

The example used in GT:SP is Mertactor, described in-book as GTL9, and
having a construction budget of 3.8 Imperial gigacredits.  The
SPA-special exchange rate at GTL9 is 3.75 CrLocal : 1 CrImp, giving a
construction budget of 14.29 local gigacredits.

Per the "Construction Times" sidebar (p63), the build rate, in CrImp, is
given as 2000 local credits converted to CrImp using the SPA-special
exchange rate - in this case, 533.3 CrImp per man-day.  This is
apparently measuring relative productivity at different TLs.  (I am
wondering what happens on GTL13 worlds - would SPA credits swap 1 for 2
like they do at market?).

The build-time example in the sidebar uses the market exchange rate,
(sidebar, p62) rather than the SPA-special rate - CrImp 400 per man-day
rather than CrImp 533.3, and cites the Mertactor starports "collectively
cost 17 billion credits".  Applying the correct build rate to that cost
would give 31.9 million man-days to build the Mertactor ports, rather
than the 42.5 million quoted.

Does that build-rate error impeach the cited total cost as well?  17 is
awful close to 3.8 + 14.29 (17.09) - was simply the wrong total cost
being used?

Otherwise, why is a figure given in CrLocal being built at a rate given
in CrImp?  Shouldn't both currencies be the same, whether CrImp or CrLocal?

Using either the CrImp total cost and CrImp build rate, or the CrLocal
versions, gives a build time of 7.2 million man-days, or 120 days using
Mertactor's available skilled workforce of 60,000.