AMCL odom_alpha1 etc settings

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Hi

Whilst I am working on trying to fix my odometry, I am finding these settings in AMCL hard to understand. I have pulled the below from the code so that we see the default, min and max settings for each one:

"odom_alpha1", double_t, 0, "Specifies the expected noise in odometry's rotation estimate from the rotational component of the robot's motion.", .2, 0, 10 
"odom_alpha2", double_t, 0, "Specifies the expected noise in odometry's rotation estimate from the translational component of the robot's motion.", .2, 0, 10 
"odom_alpha3", double_t, 0, "Specifies the expected noise in odometry's translation estimate from the translational component of the robot's motion.", .2, 0, 10 
"odom_alpha4", double_t, 0, "Specifies the expected noise in odometry's translation  estimate from the rotational component of the robot's motion.", .2, 0, 10

I note that odom_alpha5 is not relevant to me as I have a differential style robot ().

I note I am sticking to odom_model_type diff, not diff-corrected - as I dont have any reference frame for suitable values for the diff-corrected model.

So two questions really:

1) What does each setting actually mean in more natural language ? I mean odom_alpha1 I think I get - if the odometry says we are rotating, how acurate is the actual rotation in relation to what the odometry tells us - am I correct? Similarly odom_alpha_3 - if the odometry says we are moving forwards or backwards, how acurate is the actual distance traveled in relation to what the odometry tells us?

2) What are the scale of the units in each setting, ie is the robot odom says it has gone forwards 1m, does an odom_alpha3 setting of 0.2 mean we should expect it to have gone somewhere between 0.8m and 1.2m forwards?

Thanks very much Kevin