The Hidden Blade Assassin's Creed in Depth

Blocks of "health" on your DNA Synchronization Bar are earned from two different sources. I refer to these as baseline and bonus blocks.

Baseline blocks are those given to you by Al Mualim before each mission. You start with 4 for Masun, 5 for Tamir, and so on up to 13 for Maria. Altaïr does not visit Al Mualim before proceeding to Arsuf, so there's no 14th baseline block for Robert de Sable. When replaying a Memory Block, you "lose" baseline blocks to match the number you had for the first target in that MB.

Bonus blocks are earned by doing 15 View Points, Save Citizens, or any combination thereof. Whenever you do one of these "other" missions, a DNA bar temporarily pops up and fills in another cell. If all 15 cells were already filled, it rolls over to 1 cell and augments your DNA Synchronization Bar with a bonus block of health. You can view your progress toward your next bonus block at any time by pressing the Start button. The 15 cell DNA bar is in the center of the left hand side of the screen. Unlike baseline blocks, you get to use bonus blocks when replaying a MB. This is useful when doing stunt assassinations.

Here's a summary of Other Missions in the game:

VIEW POINTS
12 Kingdom (includes mandatory one outside Masyaf)
9 Damascus Poor
7 Damascus Middle
10 Damascus Rich
11 Acre Poor
9 Acre Middle
11 Acre Rich
6 Jerusalem Poor
7 Jerusalem Middle
9 Jerusalem Rich

SAVE CITIZENS
13 Damascus Poor (includes mandatory one outside gate)
8 Damascus Middle
10 Damascus Rich
12 Acre Poor (includes one outside gate)
7 Acre Middle
9 Acre Rich
8 Jerusalem Poor
6 Jerusalem Middle (does not include missing Scholars near cemetery)
12 Jerusalem Rich (includes one outside gate)

Total Other Missions: 176
Maximum bonus blocks per playthrough: 11 (= 176 / 15)
Remainder after first complete playthrough: 11 (= 176 % 15)

(Some sources say there are only 175 Other Missions. I haven't accounted for the discrepancy.)

Say you're on Memory Block 6 in the Middle District of Jerusalem with a full 20 blocks of health and your "Other" meter sitting at 15/15. If you do one more View Point/Save Citizen, your Other meter will roll over to 1/15 and you will not be credited with another bonus block of health.

Why should you care? After all, you're already at a full 20 blocks of health. Because when you Replay a Memory Block, you get the baseline blocks for that MB plus all the bonus blocks you've accumulated on this playthrough. That bonus block of health you just forfeited would come in handy should you go back and do Talal again, for example.

Here are some workarounds:

1. Go easy on the Save Citizens and View Points until you get to MB6. Totally clear the Middle District of Jerusalem while you have fewer than 20 blocks of health. Now go back and clear earlier Memory Blocks.
2. Whenever you're at full health, keep a close eye on your "Other" meter. If you see it get to 15, exit the current memory, replay an early memory, do one Save Citizen/View Point to earn a block of health, then resume your current memory.

Finally, there's a glitch where sometimes you get to carry bonus blocks of health from one playthrough to the next. You select "New Game" and face Masun with 11 or 12 blocks instead of 4. I've personally had two lucky carryovers and two where I had to start over with 4 blocks of health. So for me it has been 50/50.