Perhaps this can be a stupid invention but I find it very useful when I have to convert many dimensions from one scale to another.
It's a file in Excel (.xls) standard format so - I think - you can open it with any spreadsheet program.
The file is zipped: you must extract it before you can open it.
It has several uses:
1) it converts a size from one scale to another (if you want to rescale a part)
2) it calculates the percentage of shrinking if you want to print in a smaller scale or enlargement if you want to print in a bigger scale
3) it calculates your customized part dimension if you know the dimension of the real object
I hope it can help you saving your remaining brain cells... it worked for me! (...partially... )