How those slot number generators work

Dear Mark, I am hoping you will elaborate a bit on the Slot Machine RNG (Random Number Generator). I am very familiar with how it works.
I know those people that say, "I JUST got up from that machine, and that lady sat down, and BAM! - She hits the jackpot! - I could have won that if I stayed a bit longer!"
I know this is a totally false statement (well, not totally as it COULD have randomly happened to him had he been there) but the fact that the one lady hit it and he didn't is because the RNG came up with the winning Jackpot combo at that precise moment.
The thing that I was always confused about is WHEN the RNG stops and displays the pre-determined outcome. Meaning: If I put 1 coin in a 3-coin machine, then wait a second and put in 2 more coins, THEN hit "spin"...was the RNG continuously changing until I hit the "Spin" button? Did it stop the second the first coin was plopped in? Did it stop changing when the third and final coin was plopped in but before the "Spin" button was hit?
I have always been curious at what point does the RNG stop...with the coins being dropped (if so, which one? first or third?) or with the pressing of the "Spin" button. Tim H.

Tim, meet Tom.

Dear Mark, Something I have wondered about: When is the result of a spin on a machine determined? Is it when the first, second or third coin is inserted or when the "max bet" button is pushed? Tom M.

The RGN is constantly - well, every millisecond - spitting out random numbers, literally thousands of random number sets per second. The particular set selected by the RGN determines the outcome of each spin. It does this at the precise moment when the first coin taps the whoozis inside the slot. (Forgive the technical language.)
This is not dependent on any factors of game play, such as how many coins are bet, whether the player is winning too much money, or using Cajon voodoo or psychic trembles to decide when to hit the draw button. With all IGT games, when the "start deal" or "bet" button is pushed while playing credits, or the FIRST coin is inserted, the randomly selected outcome has already been determined, and the machine just sits around for the next bunch of milliseconds waiting for you, Tim and Tom, to decide what you'll do next.
Regarding the boon-or-bust aftermath, it's all the same whether you deposit one coin or the maximum number of coins. I get a letter a week touting the notion that the number of coins slotted somehow influences the result. It ain-t so, friends.
The outcome has been established before that first coin stops jingling. If you put in one coin and get a royal flush or a mega-jackpot, you would have got that same royal flush or those three centerline treasure chests if you had put in three or five coins.
Finally, the law requires that all slot machines have random outcomes. But be aware - there are casinos operating in places that do not have such high-minded gaming regulations. Some cruise ships operating in international waters are examples of casinos not bound by regulations.