If you've got a receipt for a Fiedler work that was purchased in French Francs, here is a chart of historical exchange rates that may be of interest to you (courtesy of Wikipedia):
| Date | # francs = $1 US | Note |
|---|---|---|
| 27 December 1945 | 1.1911 | £1 = 4.8 FRF |
| 26 January 1948 | 2.1439 | £1 = 8.64 FRF |
| 18 October 1948 | 2.6352 | £1 = 10.62 FRF |
| 27 April 1949 | 2.7221 | £1 = 10.97 FRF |
| 20 September 1949 | 3.5 | £1 = 9.8 FRF |
| 11 August 1957 | 4.2 | £1 = 11.76 FRF |
| 27 December 1958 | 4.9371 | 1 FRF = 0.18 g gold |
| 1 January 1960 | 4.9371 | 1 new franc = 100 old francs |
| 10 August 1969 | 5.55 | 1 new franc = 0.160 g gold |
| 31 December 1998 | 5.627* | Last day of trading; converted to euro (4 January 1999) |