"There's a little gauge on top, and depending on how hard you squeeze it, that's where the needle goes," Lowrie said.
The needle went to 117 when Lowrie was tested on Friday.
"It varies on which one you use," said Lowrie. "I've had a lot of variants on numbers. We've been using that same one the last three weeks, and this is my highest score."
Lowrie was encouraged enough that he expected to graduate to soft toss before Saturday's game, just the latest development in his progression.
"I'll just continue to do the work that I do and move into flips and then move into batting practice and get back into game shape," said Lowrie. "That's what I'm shooting for. It really depends on how I feel. Hopefully, there are no setbacks."
Assuming there aren't any, Lowrie expects to be back in the Boston lineup at some point in June.
"I think he's doing great," said Red Sox manager Terry Francona. "He's swinging, he's trying to throw across the diamond, he's doing everything. I think, if anything, he'll be on the good side of that curve. He's coming pretty quick.
"Now, again, he's got to hit and play. But he's doing a good job. He's here early every morning and working hard. The strength deficit in that wrist will be important. That will be the key, regardless of whatever timing there is. When that deficit doesn't become a deficit, he's going to probably be ready to go."
Lowrie's return will be highly beneficial for the Red Sox in that the current shortstop platoon of Julio Lugo and Nick Green is a little repetitive. Both players are right-handed, and both have been far more effective on offense than defense.
Lowrie is not only a stable defender, but also a switch-hitter.
Green made the start for the Red Sox on Saturday.
"It certainly makes decisions easier when you have day game after a night game, because you're always looking for energy and guys to feel good, for their bodies to feel good," Francona said. "Sometimes it depends on who's pitching for the other team. You're dealing with two right-handed hitters that basically both -- you know, there's not a lot of dissimilarity in their styles. [We're] just kind of trying to help our team win as many games as we can, using both guys."
Ian Browne is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.