Here's a clear sign that gas prices have gone upsales of manual lawnmowers, of the no-gas-necessary variety, have also gone way up. The sole domestic manufacturer of manual lawn mowers, American Lawn Mower Co., estimates annual sales of the model have more than tripled in a five-year period, going from 100,000 units to around 350,000 now. Although it is dwarfed by the nearly six million gas-powered lawn mowers that hit the market last year, a tripling of anything is nothing to be ignored. Outside of paying nothing for gas, buyers could also be drawn to the low price (around $200), the simple design which requires few repairs, or possibly the opportunity to exercise while doing household chores. Could this be a sign that change is in the air? American teenagers enjoying their lazy summer vacations are hoping not.