throw in a divide by 2 and +.5 and then you can ignore the csites if you want but labs only ever work at minimum 50% not 0%

also could be a good spot for a tip message saying you shouldnt be researching because your tpt is too low, or you could make an extra xxx points if your non cs buildings were all labs

a general tip saying over 95% or 90% is good might be ok

Efficiency = .5+([labs/2]/(land-cs))*100

that should work