If the graph text is unexpectedly small, the most likely cause is that the system display scaling is greater than 100%, as is often the case when using a high-resolution monitor. To determine whether display scaling is in fact the cause, check its value in Settings / Display / Scale and layout. If display scaling is currently greater than 100%, change it to 100%, and then exit and restart Polymeter. If the graph text is now appropriately sized, display scaling is the cause. Restore the previous display scaling and apply one of the fixes below.
The root cause is that the web browser control is not DPI-aware. An automated fix for that is available from the Polymeter download page. It's a zip archive named Polymeter-Graphviz-small-text-fix.zip, containing a REG file and instructions. The fix makes the web browser control DPI-aware for the Polymeter application only. If you prefer to apply the fix manually using the Registry Editor, follow the instructions below. Note that elevation to administrator privileges may be required.
To fix the problem for the current user only, create the following key:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_96DPI_PIXEL
and in that key, create a DWORD value named Polymeter.exe with a value of 1.
To fix the problem for ALL users, create the following key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_96DPI_PIXEL
and in that key, again create a DWORD value named Polymeter.exe with a value of 1.
The fix for all users shown above only affects the 64-bit version of Polymeter. For the 32-bit version, the key is instead:
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_96DPI_PIXEL
If the above fixes don't help, you can also try enabling the Use Cairo option.