Cover measurements were taken on both the N24 and N28 calibration blocks. Bar diameters were set to the known diameter (24mm or 28mm) in covermeter during the cover measurements. The correlation graphs from the two different diameter blocks were quite similar. Figure 4 show the results for N24 block and N28 block. The slopes of the equations (trend lines) were 0.9228 and 0.9795. The constants for both equations (trend lines) were also less than 2mm. These indicate that measured covers were reasonably accurate even without calibration. In fact, all the measured covers (without calibration) were well within [the greater of] ±5% or ±2mm as specified in BS standard.