Uppo: It ALWAYS fails with a sticky core in only one direction first. Guarantee it. Have had 48 years experience with them.
JKH: The 6850BJ has the advancer panel and can be two different gear ratios. 111:1 and 138:1. The 6850DK has no advancer panel and also comes in two ratios. 60:1 and 111:1. The DK was used for 350fpm and below and the BJ for up to 500fpm at 111:1 and for up to 800fpm the 138:1. What the 111:1 and 138:1 means is with one full turn of the vernier dial (100 divisions) the car traveled 111 inches or 138 inches. 1000frm used a totally different selector. 6104AY which covered all speeds above 1000fpm.
