There are series of NIST standard Si (640) and LaB6 (660) available, having slightly different lattice constant "a" e.g. Si 640b: 5.430940(11)
& Si 640d: 5.43159 (20).
In this case, lattice parameters are different at third decimal place. I want to know about the lattice parameter of Si standard (640a or 640b or ...) & LaB6 standard used in the FIT2D program: v12.077.
I am using Fit2D program for calibration of MAR345 Image plate (distance, tilt, wavelength etc.) with XRD data of NIST standard Si 640d & LaB6 660b.