Ggrs87/ΕΣΓΑ87

GGRS87/ΕΣΓΑ87
SetUp-Units-Map Datum- User

D(a)= + 0.0

D(x)= - (X-axis translation: -199.87m)

D(y)= + (Y-axis translation: 74.79m)

D(z)= + (Z-axis translation: 246.62m)

D(a)= + 0.0000000

Coordinate System
SetUp-Units-Position Format-User UTM Grid

Projection: TRANSVERSE MERCATOR

Latitude Origin: 0.00000

Longitude Origin: E 024.00.000

Scale (factor): 0.9996

False East: 500000.0m

False North: 0.0m

These are the numbers i have to replace, in order to convert my unit's position format from WGS84 to GGRS87 or EΣΓΑ87 witch is the Greek/Hellenic geodesic system. My unit (Garmin GPSmap 60CSx) doesn't support comma, so the only way to place the data in the ''DATUM'' section is the following:

D(x) -199.87m/-19987m

D(y) +74.79m/+74790m

D(z) +246.62m/+24662m

D(a) + 0.0000000/+00000m

You can see the divergence between the correct numbers and those that the unit allows to be placed.
I quote an example, so you can understand the divergence between the correct results (from a android app) and my unit's

Position on GGRS87/ΕΣΓΑ87 χ:533391.540
y:4531659.267

Unit's podition χ:5016741
y:4503831

Any help will very much appreciated