re the x 100 to get G/S: it's 36 seconds you need to time. Used to be used a lot in Oz with the now defunct 200MHz DME where some receivers lacked G/S info, especially if DME homing.
If you use a CR type whiz wheel you can use an off track (up to 45 deg) DME to get on track G/S. Find the difference between achieved track & the bearing to the DME. Read G/S (or time for 36 sec etc). On the wind side of the CR align the required number of degrees (using the Effective TAS scale) with the DME reading. Read on track G/S above the TAS marker. Sounds more complicated describing it than showing someone....