Mhhh ...

Let's see it closer : what's the precision of your accelerometer ??? 1% ...2% ?
so, 8 bits are sufficient...
@100 Hz ... a Pulsin 1, ... immediatly followed by a RCtime 0, ... will perfectly do the job. With no ref to the freq.

just take 1 of 2 or 3 pulses to let the PIC calculate or display.

use of the 8 bits timer in free running mode could also be seen ... as reading the timer "in flight" won't give too false a measure.

Alain