Siemens SINUMERIK 840D SL Operating Manual page 243

Incremental dimensions
In the case of production drawings in which dimensions refer to some other point on the
workpiece rather than the zero point, it is possible to enter an incremental dimension.
When incremental dimensions are entered, each item of position data refers to a point
programmed beforehand.
Example
Y
20
15
20
The position data for points P1 to P3 in incremental dimensions are:
P1: X20 Y35 ;(referred to the zero point)
P2: X30 Y20 ;(referred to P1)
P3: X20 Y-35 ;(referred to P2)
Milling
Operating Manual, 02/2012, 6FC5398-7CP40-3BA0
P2
P1
P3
20 30 20
X
Creating a ShopMill program
7.3 Fundamentals
243