Biological tissue and simulants thereof can be characterized by instrumented indentation using test methods for polymers. However, if the experiment is not well designed, the measured response can easily be dominated by the instrument, not the contact. Uncertainty analysis provides guidance for the selection of punch diameter. Or, if the punch diameter cannot be changed, uncertainty analysis tells us the most compliant material which can be tested with that punch. The analysis and test method are demonstrated for edible gelatin and bovine muscle tissue.