Well,I'm no rib expert-but I do cook with some.
Forget the digital therm method.
Seems like all the guys are saying it takes a little experience ,and some good note taking.
Smokin' likes to get folks to think about weight of your slabs.
1/2 lb difference can make a big difference-so take notes.
After a few cooks,you'll have a better feel.
Previously frozen slabs may take longer to come tender.
Loinbacks and spares may be pumped with salt water.
Today's market hog has gone up from about 220 lbs to 250 lbs+.
This now gives you about 3 lb slabs,rather than the 2 1/2 and down.
The grocery stores may promote six lb slabs,that come off an old 700 lb sausage sow,and are previously frozen, for $0.99/lb.
These could take 8 hrs at 225º.
Smokin' recommends,I believe,to put your loinbacks curl side up-with the meat toward the cooker rack.
Run the cooker @225º-250º,for a full three hours.
Now open the door.
Until you get a little experience,you will have to look and feel some.
Yes, each opening could cost you around 30 mins- or one more cold drink.
Take your ribs out and close up the cooker.
Now is the time to learn a little.
Are they pulling back from the bone ends?
If you pick up the whole slab in the middle with tongs,do the ends bend way down-where you can see the meat wanting to crack?
Can you twist the end bone off the slab with little trouble?
Will a toothpick,or your temp probe, pass easily between the ribs?
If not they need to go back in ,probably at least an hr.Maybe 90 mins.
I'd put them back in curl side/bones down to the rack.
If you are a sprayer,now could be a time to hit them with a mist of apple juice and a little bourbon.
If you have cut your slabs in half,the thinner ends may be closer to done than the thick ends.
Take notes,and remember that slightly overcooked is better than undercooked.
Well,I'll get off, before I'm accused of makin' a Smokin' post.