The pdf version of the manual can be found here.

• If the Tektronix DM5120 blinks between extreme potential values or reads –.— mV, then the sample is probably not in electrical contact with the copper blocks. Try removing the sample and cleaning the blocks then lay fresh indium strips down on them. If this does not help try applying indium directly to the sample using a wooden dowel to press the indium down firmly on the sample (take care not to touch the sample with the dowel as this may result in scratching the thin film).