I am looking at Airframe and Equipment Engineering Report No. 45 Simplified Flutter Prevention Criteria for Personal Type Aircraft. http://handle.dtic.mil/100.2/ADA955270 I haven't used a typewriter in about 25 years. I can't remember for sure, but I think the older ones didn't have + signs. Are the drawn in "things" plus signs in this equation? These symbols are found on page 15 and 18. There are normal looking drawn-in + signs elsewhere in the report. Any insight would be appreciated.