Hello,
Avl 258 and 259 schould be in HEX format, their interpretation is on Wiki:
If your 258 decimal value is 279692572557451 which converted to Hex is 0000FE61006F008B
First two bytes zeros: 0000
next 2 bytes: FE61 - X axis in mg, FE61 Hex is 65121 dec, so X axis is 65121
next 2 bytes: 006F - Y axis in mg, 006F Hex is 111 dec
next 2 bytes: 008B - Z axis in mg, 008B Hex is 139 dec
Avl 259 similary
Regards