Scale Conversion Spreadsheet
This is a Microsoft Excel Spreadsheet that can convert between different scale sizes and also between different units of measurement.
Conversion options include a number historic units of measurements. Other units can be added if you have the equivalent modern length.
When first downloaded and opened, you will be asked if you want to open the file 'Read only'. At this stage select [No] and this will allow you to save a copy that will open with the units and scale that you currently expect to use.
At this point, depending on your system and security settings, you may see a 'Protected View' warning. If so, click [Enable editing]. This will be followed by a repeat of the 'Read only' message and then a 'System security' warning that macros are disabled. Click [Enable content] and the installation will be complete.
If you don't have Microsoft Excel, the spreadsheet can be opened with 'Apache Open Office'.
I don't think this will support the macros, but those are only used to create new entries in the units table.
Click the link to download Scale Conversion Spreadsheet (36kb)