calculation app for tonearm length and countterweight

[SasquatchSoundSystem]

hello trolls

in preparation for receiving a presto 8n i wanted to mount a tonearm on the machine so that playback can be happening and analysed in real time.
since 12-16" tonearms are expensive for reasons unknown, and after talking with justin @ phonolab, i decided to investigate simply creating a longer tune for an existing tone arm.

in the research i managed to come up with this small html calculator for anyone wanting to do the same:

Download the file below from my dropbox, and just double-click it — it opens in any browser (Chrome, Firefox, Safari, Edge) on Windows or Mac with no installation needed.
Everything is self-contained, no internet connection required once downloaded.
What's in the app:

All three alignment standards — Baerwald, Stevenson, and Löfgren A — switchable at the top
Live sliders for effective length, pivot–spindle distance, cartridge/headshell mass, tube density, and counterweight mass
Six result cards: overhang, offset angle, max tracking error (colour-coded green/amber), ideal P–S distance, and both null points
Counterweight analysis showing front moment and required travel distance
Geometry diagram that updates in real time showing pivot, stylus, headshell angle, and overhang
Quick reference table for 9", 10", 12", and 16" arms (highlights the closest to your current setting)
Full dark mode support (follows your OS setting automatically)

hope it helps:

link: https://www.dropbox.com/scl/fi/k5vi1tk8scsqfiyv9swp9/tonearm-calculator.html?rlkey=m0xx6s41orz520m8xq45skj7d&dl=0

[flozki]

Nice one! Merci

[spinnertownblanks]

This is great!

[farmersplow]

Wow, great work! Thanks so much for sharing your work. I once created an Excel spreadsheet, but it wasn't nearly as good as your version. This is really easy to work with! For everyone!
Thanks,
Thomas