Harrington rears his ugly head again. An M below 30 is bad. If your down to 10 then your chance of survival is completely out of your hands and you should be call or shoving with nearly any 2 cards. At this point you need one thing only, LUCK!
M is the total cost of playing 1 orbit and is defined as bb+sb+Antes. M is totaly dependant on tournament structure and has little meaning unless you include the size of the antes and the rate at which the blinds increase. It doesn't mean you'll get to play 10 more rounds or even 10 more hands.
Most tournament players these days prefer to assess their health in terms of bb's (Big Blinds not Big Bets) as it relates more closely to the actual cost of playing a hand. A typical raise in the late stages of a tournament will be in the 2.5 to 3 bb range (4 BB's is considered an overbet and is usually indicative of hands that are likely to be problematic post flop like high pairs or 2 high cards). That said, if you bet and plan to CB on the flop the cost of playing 1 hand is going to be in the 6-8 bb range. If you started with a stack size of just 20 bb's, you're going to have to be prepared to invest a minimum of 1/3 of your stack, and that's if you get no post flop action. If you do see any action you may find yourself pot committed with any piece of the flop or strong draw. That's why even 20bb's deep your best option may be to open shove with any playable hand.
30bb's is far from optimal but at least you have the option of getting away from a bad situation. However, just getting involved in a hand that turns sour drops you down into the danger zone.
At 40bb's your sitting pretty and have all your tools at your disposal. You can raise, 3 bet, chase draws, play speculative hands like suited connectors and small pairs or just sit back and wait for premiums.