Your Invoice





202 Atlantic Ave New Hyde Park NY 11040




Customer: Joe Sample





Address: 123 Main St Garden City NY 11530



Phone: 516-555-1212


Item Purchased





Wilson Pro Staff Mid s/n 012763 (2)


Wilson Sensation 16 @ 55lbs Constant Pull (DT=41)




12.5 ozs.





Restrings to date: 3





Days since last strung: 85





Tension Loss: 27%


























Amt Paid:






Balance Due:


In the invoice above, Joe Sample has had a Wilson Pro Staff Mid (serial number 012763) restrung with Wilson Sensation 16 gauge string at 55 lbs. The tensioner was pulling in "constant pull" mode. Dynamic tension is 41. The racquet weighs 12.5 ounces, is balanced 7/8" headlight, and the swingweight is 314. This is the third restring for this frame, it's been
85 days since it was last restrung and the strings we cut out  lost 27% of their original tension.

Explanation of Invoice Features

Serial number: Most major racquet manufacturers include serial numbers somewhere on the frame. Some are on the decals in the throat area, some are stamped into the butt cap. Sometimes they are printed on the edge of the hoop. You will find the serial number on your invoice immediately after the racquet name.

Alt serial number: If you have two or more identical frames, regardless of whether they have serial numbers, I create a secondary serial number which shows up in parentheses on your invoice immediately after the mfrs serial number and on your racquet label as shown circled below. On the Your Account page this number displays in the column "ALT".


Tensioning mode: The phrases "constant pull" and "lockout" refer to methods of tensioning. For more on this please click here.

Dynamic Tension: Immediately after stringing I test and record string bed stiffness with 3 different meters. The Dynamic Tension reading is produced by the Beers ERT700 and is defined as the number of kiloponds required to deflect the string bed 1 centimeter. In this case the reading was 41. It is usually a good idea to restring when string bed stiffness has dropped 20% from the initial reading. The chart below should give you a general idea of where your initial reading falls within the ERT's range. These readings however apply to tennis racquets only .

Dynamic Tension


45 and above

Extremely tight. Boardy feel.


Very tight





Below 30



Weight: This is the weight of the racquet after stringing, expressed in ounces.

Balance: A standard length tennis racquet is 27 inches long, so if it were evenly balanced the balance point would be at 13-1/2 inces. If it balanced at a point 14 inches from the butt cap the racquet would be 1/2 inch head heavy. Another way to look at this would be that if you cut the racquet in half 13-1/2 inches from the butt cap, the upper portion of the racquet (head) would weigh more than the lower portion. Similarly, if the racquet balanced at a point 13 inches from the butt cap, the racquet would be 1/2 inch headlight.

Swingweight: Probably the most important of the frame statistics because it is entirely possible to have two or more frames with the same exact weight and balance yet different swingweights. Swingweight is a measure of your racquet in motion. Too high a swingweight and the racquet is difficult to manuever, too low and your shots lack penetration. Prior to August 2007 I used the Pacific Multitest Computer to measure swingweight. These days, I am using a Prince Precision Tuning Center.  The Prince machine has the advantage of reading out in kgs/cm², the industry standard.

Restrings to date: Nothing you do during the course of a match (short of throwing your racquet) is as strenuous for it as restringing, so it's lifespan is pretty much determined by the number of times it gets restrung. I don't have any rules of thumb to offer here, but if you have more than one frame, you might find it useful to know which one is the least worn, etc.

Days since last strung: Literally the number of days the previous stringing lasted. If string breakage is not a problem for you, you might want to take advantage of the increased playability of thinner strings. If you are breaking strings frequently, you might want to look at thicker strings or strings designed for durability.

There are several rules of thumb for deciding how long to wait between stringings. One is that you should string your racquet as many times in a year as you play during a typical week. Using this guideline, if you played twice a week, you would string twice a year. Another rule of thumb is to restring after 40 hrs of play. If you find yourself wanting to smash your racquet to smithereens, that is also a good indicator that it is time to restring. You might also want to visit my shop and have the string plane stiffness checked. Low readings are a definitive indicator that it is time to restring. Historically, most customers find their racquets difficult to control once the string plane stiffness readings fall below 30 on the Beers ERT-700 or 48 on the Pacific Multitest Computer.


Tension Loss: I re-test the stringbed stiffness with the Beers ERT-700 when you return the racquet (assuming the strings are not broken) to calculate the percentage of tension loss since your last stringing. The string industry recommends re-stringing after a 20% tension loss. In the sample above, the strings have lost 27% of their original tension in 85 days. Joe's game would probably benefit from more frequent visits.