Help with Custom Column 'Mobi Size'

[LizPhillips]

Hi, I have changed from the Kindle Keyboard to the Paperwhite and since I now have a lot less storage space, I have just about used it all up!! Only 100Mb left.

I'm pretty sure some of my earlier book conversions are not using the most efficient format for storage size, plus I have converted some using the 'both' option on the MOBI output.

I have read that the default Size Column gives the size of the largest file & I'd like to create a column which displays the size of a book for a particular format (mostly MOBI) so I can give reconversion priority to the largest books.

I'm afraid I'm not terribly good with template functions & creating custom columns so if anyone can post some instructions or point me to a previous post I'd appreciate it