What's the logic/ history behind the series names for Agilent instruments?

Zsuzsi, the LC/MS instruments follow a Gxxxx model number code. For LC/TQs (including the 6495 series) we use 6400. SQs use 6100, TOFs use 6200, and QTOFs use 6500. 

For the LC/TQs, the rule of thumb is the higher the number the better performance.

For example, in order of increasing performance: 6465 (Ultivo) < 6470 < 6495 

Zsuzsi, the LC/MS instruments follow a Gxxxx model number code. For LC/TQs (including the 6495 series) we use 6400. SQs use 6100, TOFs use 6200, and QTOFs use 6500. 

For the LC/TQs, the rule of thumb is the higher the number the better performance.

For example, in order of increasing performance: 6465 (Ultivo) < 6470 < 6495 

Thanks mipastor, that makes a lot of sense.

But why? I mean, how did these numbers come about? Is it an inheritance from the HP days? 
Why do the numbers increase by x, instead of y?
Are they in some way reflective of performance increase?

I think I understand the first number, where an LC starts with 1; GC: 5; MS: 6; GC +MS/MS 7 (?)... but what about the following numbers. 
Also, what is the significance of the additional a A B and C tags? 

Haha. Sorry for being annoying. 
It's unlikely for me to go to work on any given day think, "Let's call this MS 6495!" 
Again, it's really not important, just wondering.

Thanks for taking the time to answer.   

PS. Your explanation of the second number just sank in... a bit of a delay from my part. Sorry. 
So the question is really just the last two numbers and the letter. 

I am not sure I can answer the "Why?" in terms of the number increase and how they are positioned relative to performance. 

The first LC/TQ was the G6410A in 2006. Each time there is a new release (some improvements) of the same instrument, there is a letter revision (6410A -> 6410B). These instruments may be based on the same chassis but include some hardware differences warranting a letter revision. A later letter (in the alphabet) suggests a newer model.

In general, the higher the number, the better the performance but this may not always the case. 

The current LC/TQ portfolio is as follows (in order of instrument performance):

G6465B (Ultivo B) < G6470B < G6495C

I hope this helps. 

Yes, that's great. Thank you.