Laser centre finder with interchangeable collars

Laser centre finder for milling machine, drill press etc.
I designed it so that it can be fitted/removed without needing to remove the chuck or tool from the machine.
I designed this with replaceable collars so that the same centre finder can be used on different sized spindles (ie my mill has a 40.6mm diameter spindle and my drill press has a 36.6mm spindle).
The collars just press onto the spindle from the side.
I used a DIL/DIP switch. This was a 2 way DIL switch which i sanded half away to make a single DIP switch (eg https://au.rs-online.com/web/p/dip-sip-switches/8772113/)

One leg of the DIP switch passes directly into the battery cavity to make the negative contact, the other leg is soldered to the negative laser wire.
The positive laser wire passes into the battery cavity to make the second contact.
I used 2x SR44 batteries for their stable voltage and high current.

To use:
Attach to the machine spindle, and angle the laser toward the centre of rotation
Turn the laser on
Start the spindle. the laser will trace a circle.
Adjust tool height to change the size of the circle traced.
Align part or hole etc to the circle of light.
To centre on a cylinder, project the light onto the side of the cylinder: when centred on the cylinder, the line of light will be horizontal as shown, and if off centre will be at an angle.
If yo want to centre on a point raise or lower the spindle to decrease the size of the circle until it becomes a spot (may need to adjust the angle of the laser).

The advantage of this design over a "crosshairs" laser alignment tool is that the crosshairs concept can only be used to align to a point: you cannot centre on a hole or cylinder etc.

If you make this, please post your make.
All tips are very greatly appreciated, particularly as this design took quite a lot of work to refine and get to work as well as it does.

UPDATE: Aug 2020:
Since making this and using it on a number of projects, I am amazed at how accurately it can be used to centre on a hole or cylinder. For example drilling a hole into the end of a cylindrical boss. While it is not intended for "1um" accuracy, it can easily get 0.1mm (0.040") centring accuracy (or better) without any effort.