There are always exceptions but it is usual to configure a machine’s axes with relation to the position in which the operator will stand.
The axis moving left – right being the X axis and the axis moving toward – away being the Y axis.
The physical direction of each axis is defined in Mach3 according to the direction the tool moves over the work.
The tool movement to the right of the work is +X
The tool movement to the left of the work is -X
The tool movement to the back of the work is +Y
The tool movement to the front of the work is –Y
And just for completeness…
The Z axis movement with tool moving away from work is +Z
The Z axis movement with tool moving towards the work is –Z
And X0 , Y0 is in the front left hand corner.
Please check out the Mach3 Manual for more details.
http://www.machsupport.com/help-learning/product-manuals/Tweakie.