Excel VB.NET to PHP Replica

I have an in-house Excel workbook backed by VB.NET code that drives day-to-day operations. Every formula, macro, and hidden sheet already does exactly what I need, and I will give you that file together with a written specification. Your job is to reproduce the same behaviour inside a browser using custom-written PHP and a MySQL database—no framework such as Laravel or CodeIgniter, just clean, well-documented vanilla PHP.

The new system must let users sign up and log in (email + password), enter data through easy web forms, run all the existing calculations server-side, then present the outcomes through printable reports and on-screen charts. I rely heavily on look-ups, conditional calculations, and multi-sheet cross references, so accuracy of the math is critical. For the reporting layer you are free to suggest libraries (e.g., Chart.js, Highcharts) as long as the visual look can match or improve on the Excel originals.

Deliverables
• SQL script to create all tables and sample data
• Fully commented PHP source replicating every calculation from the workbook
• Responsive HTML/CSS/JS front-end with data entry screens, report views, and basic navigation
• Simple authentication module (registration, login, password reset)
• Migration guide explaining how to deploy the system on a standard LAMP stack

Acceptance criteria
• Results produced by the PHP version must match the workbook outputs cell-for-cell on a provided test set
• All pages load without errors in the latest Chrome, Firefox, and Edge
• Code passes a brief security review (prepared statements, no exposed credentials)

Once the replica is validated, we can discuss phase-two feature ideas, but for now the brief is a faithful, bug-free port.