to purchase some unassembled Calibre 3019PHC movements in 1981, which Zenith assembled out of leftover spare parts. Rolex expressed interest in using the 3019PHC to power a new series of Daytonas, but would not award the ten-year contract to Zenith until they could resume production of new movements. Production resumed in 1986 after Vermot showed company leaders where he had saved the tooling and production notes. Rolex modified the movement by reducing the beats to 28,800 VPH to increase the power reserve, and made a few other changes, retaining only 50% of the original parts. The modified movement was designated Calibre 4030 by Rolex. The second series Daytonas used a sapphire crystal (in lieu of the acrylic crystal of the original series); the case diameter grew from on the original to for the second series; the dials were now glossy; and the sub-dials were now largely the same color as the dial, with an outer track in a contrasting color. These later series Daytonas, pre-dating in-house movements, were accurate and reliable; they were produced in limited quantities from 1988 to 2000. The second series uses a five-digit Reference number. The "Chairman Daytona" was created in 1991 as a variant of Reference 16528; it has a galvanised blue dial and the tachymeter markings go to 400 units/hr. Two second series Daytonas were sold with leather straps: Reference 16518 (yellow gold) and 16519 (white gold). Third series The third series, introduced in 2000, has a movement made by Rolex (designated Calibre 4130) and a six-digit model number, Reference 116520. Externally, the third series may be distinguished by close examination of the dial; the two sub-dials at the 3 and 9 o'clock positions are now slightly above an imaginary line drawn between the 3 and 9 o'clock chapters, and the running seconds sub-dial has been relocated from the 9 o'clock position to the 6 o'clock position. The six-digit Daytonas are certified, self-winding chronometers with chronograph functions. Rolex has sponsored the 24 Hours of Daytona sports car race, which became known as Rolex 24 at Daytona, from 1991, and named its chronograph watch after the race. Stainless steel variants of the Daytona remain very difficult to acquire, and a waiting list exists for interested purchasers of new watches, as production is limited to a few thousand per year. Daytona "Paul Newman" dial The rarest Daytonas are those with what has been called the "exotic"