I saw a HP-48SX at flea market and I couldn't resist.

[jebem]

(05-21-2014 04:16 PM)Massimo Gnerucci Wrote:  Here the mean 1990 exchange rate PTE/USD is given as 142.555

Apparently it shows a large deviation from what the original owner has paid in PTE.
Because I use to travel quite a lot to outside the Euro zone, I use this currency converter site that also allows historical search.
It came out with a closer value of 131.764 for Dec 3, 1990, which is a closer match, assuming that the calculator was acquired in the beginning of December, that is.

Period Average 131.760
Period High 135.871
Period Low 130.115

Dec 24, 1990 - Dec 30, 1990 135.871
Dec 17, 1990 - Dec 23, 1990 132.808
Dec 10, 1990 - Dec 16, 1990 130.464
Dec 3, 1990 - Dec 9, 1990 131.764
Nov 26, 1990 - Dec 2, 1990 131.380
Nov 19, 1990 - Nov 25, 1990 130.115
Nov 12, 1990 - Nov 18, 1990 130.431
Nov 5, 1990 - Nov 11, 1990 131.244