Complex sentence: Instead, students went through as many TLU's as they wished (a TLU was completed by taking a multiple choice test on IBM style computer cards) but were expected to complete at least one TLU per week.
Split into simpler sentences: Instead, students went through as many TLU's as they wished (a TLU was completed by taking a multiple choice test on IBM style computer cards). Pupils, however, were expected to complete at least one TLU per week.