A voltmeter was standard 'approximately' 2000 to 2006 with the four small gauges in a row dash. I have one on my Roadster but I'm not entirely convinced it's accurate.
The voltmeter in my S1 Roadster barely moves whatever current is being drawn or put back. I'm having a new one fitted at my next service. A new one from MMC is only £29.95 including VAT and matches the original one in appearance.