The Drop Weight tests (DWT) by JK is now replaced by the JKMRC Rotary Breakage Tester. It is faster as confirmed by Tony and now used by many since its intro http://www.min-eng.com
In an AG/SAG mill there are two main mechanisms of breakage, namely impact (high energy) and abrasion (low energy). The industry accepted JK
impact breakage parameters, A and b, can reliably be determined using the new generation high throughput JK Rotary Breakage Tester® (JKRBT®).
 Drop Weight Tester |  Rotary Breakage Tester |
Here is a download link to a pre-build Excel file you can use in testing for with a Rotary Breakage Tester to obtain the data from which JKMRC uses to calculate A and b. This format was used for Hardness Geometallurgy testing
AxB-JKMRC-Rotary-Breakage-Tester-Test-Form
I find great about drop weight testing.