SWM Calculations Confusion

Picture of Eric Strom
Re: SWM Calculations Confusion

Hi Darren,

I don't have an explanation for the second grade item, yet. I would be interested to see a screenshot of the categories and items page as well as the settings for the course category in order to investigate further. Do you have the course category in the gradebook set to drop any scores?

Also, what version of moodle is this running? Worth noting if this is all tied to a bug in a particular version - although I'm not aware of any grade calculation bugs off the top of my head.


Picture of Darren Hall
Re: SWM Calculations Confusion

Hi Eric,

We're running 2.3.8.

Here's a screenshot of the Categories and Items Full View.

categories and items full view

Nothing out of the ordinary that I can see.  The bracketed 46 threw me off at first, but when you look at the scale used (see screenshot in response to Emma's post), the 0-30 with .5 increments scale only starts using the half point increments above a score of 15.  So, the 46 appears to represent the number of increments in the scale itself (it's not clear to me why this is important or useful info to show in the grader report, but there you have it).

As far as the course category settings are concerned, I'm not entirely sure where you are suggesting I look.  Here's a screenshot of the course category settings page for that category that I'm aware of, but it doesn't have any settings that impact the GB, so I'm guessing you're referring to something else.

course category settings


Thanks for helping me to troubleshoot this issue.



Picture of Emma Richardson
Re: SWM Calculations Confusion
Documentation writersParticularly helpful MoodlersPlugin developers

I have never used increments but here is what is happening - you say .5 increments start at 15 - so a grade of 21 if each point after 15 equals .5 brings an actual total of 18 which is exactly 60%.

Well, the math works at least!


Picture of Darren Hall
Re: SWM Calculations Confusion

Thank you, Emma!  That does actually solve the mystery and it highlights for me the perils of using scales because it appears they don't work at all the way one would intuitively expect.  In the example above, it would appear the actual SWM calculation that Moodle is using is based on the number of increments rather than the point values associated with those increments.  Here's what we came up with (my more math-literate colleague helped me get to this):


So, the math checks out in the end.  But I can't for the life of me see the value in scales that don't have uniform increments (there are several in the standard scales set.  Indeed, the only value I can see to any numerical-based scale is in the case of needing to create an activity with points greater than 100 (a separate conundrum).  Is there a way I can disable these scales?  IF I did disable them, does anyone know how that would affect grades based on those scales?

Picture of Bob Puffer
Re: SWM Calculations Confusion
Plugin developersTesters

I have no idea how 'increments' are implemented in scales for a gradebook. My understanding of scales is that every comma-delimited value represents a value of 1, starting at zero before the first comma.

My guess is the collaboration is off because its the farthest from the point at which you say you begin incrementing scale values by 5. 

That said, Moodle's core gradebook assumes you will want your categories and course total to have a range of 0 - 100 so it scales everything accordingly which I feel is ridiculous since that is no more than a restatement of percentage. 

Picture of Robert Russo
Re: SWM Calculations Confusion
Plugin developers

Bob's right.


Scales are screwing you up.


If you;re using numeric grades, don't use scales.


In your case, the max grades are not what you expect them to be for your scale, therefore messing up your SWM calculation.