Difference btwn Sous Vide Mode & Low temperature bake with 100% steam?

I followed a regular roast beef recipe calling for 200F conventional bake for internal temperature130F (around 3-4 hours for conventional oven). However, I did add 100% steam, for I wanted softer and tender texture.

At the meant time, I saw a APO roast beef recipe calling for Sous Vide mode with same internal food probe for 130F for 27 hours.

I was curious about the sous vide mode recipe but did not have 27 hours to try it out during dinner time. Thus, out of curiosity with limited time, I turned the sous vide mode on during the roasting process. Strangely, the oven temperature reading changed from 200 to 186. Hm… I thought I was reading it wrong, so I turned the sous vide mode on and off to check the oven temperature.

Indeed, whenever the sous vide mode is off, it read 200, yet 186 with it on every single time.
Q1. I don’t undertsand this concept: whatever the oven temperature is a fact; how come temperature reads differently between sous vide on or off?

Q2. Out of curiosity again, would this roast beef recipe for APO calling for 135F with sous vide mode on for 27 hours result in the same or at least similar taste, texture, and healthy benefit, if baked with sous vide mode OFF at the same temperature 135F with 100% steam???

Thanks

Learn sous vide. Read Douglas Baldwin’s A Practical Guide to Sous Vide Cooking.

https://douglasbaldwin.com/sous-vide.html

I just did a sirloin roast today, cooking it in sous vide mode at 132F for 8 hours, followed by a quick sear on the grill. It’s perfect for a busy day, since you can start it in the morning and it’s ready whenever you want it in the evening with little fuss to finish. The probe was at 133F in about 3-4 hours.