strange 34465a IV test result

[analogNewbie]

34465A is set to 10V range, input Z auto.
B2987A provides voltage to 34465A, and measure current.

V(volt)   I(pA)
0      7.1
1      9.1
2      10.2
3      11.1
4      13.1
5      15.2
6      15.5
7      15.7
8      14.8
9      13.8
10      12.2

It's strange that the current gets smaller when V>8.

[Kleinstein]

The input current does not have to be a linear function of the voltage. Especially the current from charge injection due to Az switching can be nonlinear and possibly getting smaller with higher voltage.

[analogNewbie]

Thanks
The data is much better after turning off auto zero
V   I
0   1.0
1   1.9
2   2.0
3   2.0
4   2.7
5   4.1
6   5.3
7   6.5
8   7.6
9   8.6
10   9.9