A state-of-the-art handheld diagnostic scanner issued aboard larger Starfleet ships in the 2380s, coveted by the engineers of the USS Cerritos, who have to make do with older equipment.
The T-88 is a new model of engineering scanner, far more capable than the tools carried on a California-class support ship.
It appears in the Lower Decks episode Cupid's Errant Arrow. The Cerritos is assisting the much grander USS Vancouver, and Sam Rutherford and D'Vana Tendi are thrilled to find its engineers equipped with T-88s. A Vancouver officer sets the two friends competing against each other with the promise of a reward for whoever finishes the work first.
The reward turns out to have a catch, a transfer to the Vancouver that neither of them wants, and the pair are happy to return to the Cerritos together, their enthusiasm for the T-88 undimmed.