presence of hydrocarbons, page-11

http://webapps.rrc.state.tx.us/DP/drillDownQueryAction.do?fromPublicQuery=Y&name=O.B.%2BRANCH&univDocNo=485947914

this is a link to the permit application for O.B. Ranch #1 ...

q: for the O&G experts out there ... why do explorers seem to be quite imprecise with their depths? TD is stated to be 16,000 ft in announcements but in the application they have applied to drill to 15,500ft ... not that the additional 500ft means much to me BUT can someone confirm if it is normal practice to be imprecise with depths? Would mean that I could stop trying to make sense of drilling reports such as those from FP which were quite confusing on the way down in terms of what was primary TD and secondary TD etc etc.

thanks in advance ...