The Swiss Performance Index SPI is Switzerland's most closely followed performance index. It is a dividend-corrected index that includes all SWX Swiss Exchange-traded equity securities of companies domiciled in Switzerland or the Principality of Liechtenstein. Paid prices are taken into account in calculating the SPI as a whole. If no paid prices are available, the index is calculated on the basis of bid prices. The index is recalculated and published every three minutes. On 1 June 1987, the SPI was standardised at 1000 points.