But larger drives specifically have seen the biggest dip since the beginning of the year, in relation to smaller capacities. For instance, at the start of the year in January 2012, the price-per-GB cost of a 256GB SSD was $1.37/GB. By September, that price had dropped 65% to $0.48/GB.
The digital handheld tachometer is a gauge for determining speed, velocity and distance. This handheld tachometer measures in two ways: either optically and therefore without contact, or mechanically via various adapters.
Measure the distance in millimeters between the two marks. This is your PD. Repeat this process a couple of times to ensure you have an accurate measurement. If you have a willing assistant, you can simplify the process even further by having your friend measure your PD using a ruler.