Officially the error range of the 400 Series cameras is 1% or less. In practice, it may vary depending on how close or far the camera is to what it is observing. For example, depth measuring accuracy may reduce when observing objects at a distance of 3 meters or more.
Depth accuracy may also reduce if you use a resolution lower than 848x400.
At close range, you can try altering the scaling factor of the camera to get the best results.
I think this is what we need:
"The default scale of a D400 device is one millimeter, allowing for a maximum expressive range of ~65 meters. The depth scale can be modified by calling
RS2_OPTION_DEPTH_UNITS, which specifies the number of metres per one increment of depth. 0.001 would indicate millimeter scale, while 0.01 would indicate centimeter scale."