It has been noted that 1 point equals 1/72 of an inch. The screen I am currently using measures 1200 pixels in height on a 20cm frame. When projected, those same 1200 pixels span out to cover 3 metres.
The W3C CSS specification contains numerous measurements, although only a few are utilized correctly.
Your optimal choice is to utilize em's for layout purposes as they are closely tied to the font being used. Percentages can also be effective.
However, adjustments may need to be made in browser layouts by a small amount, particularly when dealing with buttons, dropdowns, and text boxes. This often involves setting something to position relative in order to slightly adjust its placement up, down, left, or right. Common instances of this occur when there are slight discrepancies between IE and Firefox.
Aiming for uniformity in form rendering across all screens and projectors is quite ambitious, suggesting that different browsers will display content identically.