## Checkpoint

### which two layer-lines (LL) were used?

Note, there may be multiple acceptable answers to this question. Format: LL (R, Z)

LL (15, **44.5**)

LL (15, **16.5**)

Hint: LL (???, **122**) = 2* LL (15, **44.5**) + 2* LL (15, **16.5**).

LL(**122**) is close to meridian, meaning it has to be a very small Bessel order. So, LL(**44.5**) and LL(**16.5**) must have different hand. In other word, one is "+" and the other is "-"

### What are the possible Bessel order ranges for those two vectors?

LL (15, 44.5)
:

2*π*R*rmax = 2 * 3.14 * (15/1024/0.85) * 151 = 16 Bessel order n ≤ 14

2*π*R*rmin = 2 * 3.14 * (15/1024/0.85) * 80 = 8.6 Bessel order n ≥ 7

LL (15, 16.5):

same range, 7-14

### What are the possible symmetries?

### What's the correct symmetry (quickly check whether it is in your list)

point group: C1

helical rise: 1.04Å

helical twist: 26.2 degrees