Re: Questions

Arm BP Monitors are considered to be the most accurate and probably those recommended by a Heart foundation, as they are here in the UK.

Ideal BP is supposed to be 120/80 but tends to rise with age, generally speaking. BP will also fluctuate during the day in response to stimuli such as anxiety/stress, so a reading is best taken first thing in the morning on arising from a resting state.
A big drop would be somewhere in the region of from 130/90 to 90/60 or lower on the following day, but BP should drop on a gradual basis over time, rather from one day to the next.

Yes I would check your resting BP before the fast begins and as a guide, but accuracy is probably best when readings are taken over a few days, and at the same time of day as mentioned, rather than just on one single day/reading.

Chrisb1