> Does anyone know which datum is being used for the topographical maps
> issued by the Dutch Topographical service?

There are three different datum used for the maps from the TDN.

1) WGS84 in combination with the UTM grid. The use of WGS84
   is indicated in red "WGS84"
2) Other UTM maps use the ED50 datum
3) A special "Dutch only" grid (RD;Rijksdriehoekscoordinaten).
   In the RD grid, the east-west coordinate has a value between 0-300
   and the south-north between 300-620
   The OLV church in Amersfoort is the "center" and has
   the coordinate 155000;463000

It can be used on a Garmin by setting the user grid and user datum:
User Datum (WGS84-local)
DX: 593 meter
DY: 26 meter
DZ: 478 meter
DA: 740 meter
DF: 0.1003748

User Grid
Longitude Origin: 5º23.258 East
Scale: 0.9999079
False Easting: 155000
False Northing: -5316592

--
Wim Joppe
joppe@xs4all.nl
______________________________________________________
 
ADDITIONAL INFORMATION
For use with a Magellan 320 -From Jacek M. Holeczek
 
Bessel 1842 user datum:
(WGS84-local)
dx : 593m
dy : 26m
dz : 478m
da : 740m
df : 0.1003748
 
Dutch RD User Grid:
Choose "Trans Merc" (other options: Lambert Con, Stereograph, Oblo
Merc and Polyconic)
Latitude of origin: 52.15617N
Longitude of origin: 005.38763E
scale factor: 0.99990790
units to meters conv: 1.0
false easting at origin: 00155000.0
false northing at origin: 00463000.0

Jan Kleynjan, Wageningen