When VMs won't keep an IPv4 address

Today while troubleshooting Internet slowness on my laptop I noticed that a virtual machine I had running lacked an IPv4 address. It had an IPv6 address and could connect to some sites including the host machine. After some stumbling around I found this Ask Ubuntu answer which mentioned clock skew. Sure enough, my modem/router's time was an hour off, possibly due to automatic Daylight Savings Time adjustment being disabled? I fixed that and made the VM reattempt DHCP configuration. It got an IP address, but with a very short lease. A little while later I found that its IP became the same as the host's, which was concerning. I only got it to hold onto a unique IP by adding a DHCP reservation in the router settings.

Measuring mouse sensitivity

While writing the Super User answer mentioned in yesterday's post, I needed to measure the ratio of physical mouse movement to pointer movement, making sure my 1:1 acceleration curve was actually equivalent to the desired unaccelerated setting. One of the posts I linked supplies a ZIP file which contains a MouseMovementRecorder ZIP file which contains a program that prints every mouse movement. I launched that program, made a very sudden horizontal or vertical mouse movement, and identified an output line with large distances. Dividing the large component of the "pointer movement" column by its counterpart in "mouse movement" produced the desired ratio, 2.5 by default on my system, though it probably varies by DPI. After setting an acceleration curve with a different slope, I measured again to make sure the ratio was scaled by the desired factor.

Setting an arbitrarily precise mouse sensitivity

The Mouse Properties dialog has a slider with discrete tick marks for setting the mouse sensitivity. The MouseSensitivity value in HKCU\Control Panel\Mouse has twice the resolution but is still an integer, with a range from 1 to 20. The mapping of that number to sensitivity multiplier is tabulated here.

It is possible to set an arbitrarily precise sensitivity scale by taking advantage of the SmoothMouseXCurve and SmoothMouseYCurve values, which are consulted when "enhance pointer precision" is on. These are explained in great depth in this article, but in summary they are a set of points that describe a piecewise linear function of physical mouse speed to pointer speed. If the curve is changed to a straight line, the fancy pointer-precision-enhancing effect is disabled: a mouse movement's distance alone, not speed, determines the pointer movement distance. Since the curve points are 16.16 fixed-point values, there are far more than 20 options for the slope. Starting from a curve equivalent to the default sixth tick (provided by this site)...

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Control Panel\Mouse]
"SmoothMouseXCurve"=hex:\
    00,00,00,00,00,00,00,00,\
    C0,CC,0C,00,00,00,00,00,\
    80,99,19,00,00,00,00,00,\
    40,66,26,00,00,00,00,00,\
    00,33,33,00,00,00,00,00
"SmoothMouseYCurve"=hex:\
    00,00,00,00,00,00,00,00,\
    00,00,38,00,00,00,00,00,\
    00,00,70,00,00,00,00,00,\
    00,00,A8,00,00,00,00,00,\
    00,00,E0,00,00,00,00,00

...all Y values can be multiplied or all X values can be divided by the sensitivity multiplier of choice. Only the first 4 bytes of each line matter, and they're in little-endian. A logoff/logon cycle may be necessary for the change to take effect.

Based on my Super User answer.