Yeah, two clocks with two separate blind progressions. Two separate tourneys, each tourney is seven people.
I use BlindValet and, because of my line of work, I have spare computers and laptops all over the place. You can also run it on a smartphone or tablet.
The first three people sitting out aren't part of the first tournament at all; they never drop into it. They're just waiting for the second game to start, which will start as soon as four drop out of the first tournament.
Instead of running, say, three 10-player tournaments, you'll probably six or maybe even seven 7-player tournaments, because you start the second tournament before the first even finishes, and you often have two running at once. You may even get 8 in, because 7-player sit-and-go is inherently faster per person than a 10-player sit-and-go (fewer player decisions per deal.)
If my math is right, a group of 10 players doing repeated 10-player tournaments will, on average, have four people sitting out. A group of 10 players with two tables playing a Seven-Up tournament will, on average, have less, 3.25 people sitting out. In Seven-Up, even when you account for three extra people sitting out at the start and finish of the night, you'll still have less than 4 people sitting out, on average.
Crap, now I have to prove that last part to myself... that it's still less than 4 people sitting out even when you account for the opening and closing lag...
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OK, here's a side-by-side for a Regular 10-player tournament (whether it's on one or two tables) and a Seven-Up! tournament with 10 players on two tables.
For the Regular side, on the left, first column is the number of people in the game, and the right is number sitting out.
For three full tourneys, you average 4.0 sitting out per "stage."
On the Seven-Up! side, there's a column for the number of players in each Tournament, and in the middle, the number of people sitting out. Assuming almost the same number of "stages" as for three Regular tourneys, you'll get in six Seven-Up! tourneys, and average only 3.77 people sitting out, even assuming all ten player show up right on time and you start the night with exactly three sitting out.
(Green highlight shows the start of a new tournament.)
Six-Up! does even better, on that measure. Only 2.38 people out, on average.
View attachment 6084
It's basically two 6-player Sit 'N Go's. Much easier to explain that way.
Probably works well for about ten players, give or take one or two.