Some research suggests other estimates to the accepted workforce size. For instance, mathematician Kurt Mendelssohn calculated that the workforce may have been 50,000 men at most, while Ludwig Borchardt and Louis Croon placed the number at 36,000. According to Miroslav Verner, a workforce of no more than 30,000 was needed in the Great Pyramid's construction. Evidence suggests that around 5,000 were permanent workers on salaries with the balance working three- or four-month shifts in lieu of taxes while receiving subsistence "wages" of ten loaves of bread and a jug of beer per day. Zahi Hawass believes that the majority of workers may have been volunteers. . is estimated that only 4,000 of the total workforce were labourers who quarried the stone, hauled blocks to the pyramid and set the blocks in place. The vast majority of the workforce provided support services such as scribes, toolmakers and other backup services. The tombs of supervisors contain inscriptions regarding the organisation of the workforce. There were two crews of approximately 2,000 workers sub-divided into named gangs of 1,000. The gangs were divided into five phyles of 200 which were in turn split into groups of around 20 workers grouped according to their skills, with each group having their own project leader and a specific task.