The 1146A is now obsolete and the data sheet for the 1146B states that it is form, fit and function equivalent to the 1146A. What is the difference? Is this a RoHS issue or was the design improved with newer components, even though the performance is the same? It would be helpful if Agilent made more clear the differences between "B" and "A" models so customers are educated on the changes, even if they are cosmetic or for manufacturing reasons. Thank you!