Hmmm ... I don't know. The way we look at it, the yard still has certain costs which are the same whether you are out for 4 days or 7 days i.e. admin staff, cleaning, laundering the bedding and towels if supplied, refreshing the little starter supplies, handovers etc. If you add this as a static charge to the hire cost for the number of days then that must be part of why it's never going to be a like for like per day. Just my take on it but there are many people better qualified than me to answer that.