तपर is a letter with तकार around. तपर also eclipse the सवर्ण but they don't indicate different काल. For example, in अदेङ्ग् गुणः, both अत् and एङ्ग् are तपर and therefore, they eclipse the six ह्रस्व रूपs - e.g. अकार eclipses अ,अँ,अ,अँ,अ',अँ' forms.
Thus, देव् ऐस् becomes देवैस्.